i wonder why one should not prefer Nikon over Canon !!

like asking why one should not prefer Film over Digital (TTL over non-TTL light metering) or... non-OPTIMAL (slower) systems over OPTIMAL (faster) systems...

by your own preferences, it isn't sufficient to make it preferable to others

the number of AF points don't mean much unless it works under conditions of its users (bright high light vs darker/dimmer low light).

with shooting conditions/objectives 'equal' (same distance/same FOV/same framing composition/same DOF (high vs low)/same shutter speeds (non-blur vs blur)/same noise levels (low vs high))... some systems will have advantages due to different lens-body-sensor size configuration (small vs large)

any AF system with its sensors closer to the lens opening (DX/APS-C/or smaller) should perform better than one with its sensors farther away (FX/FF)

any AF system with inherently greater DOF (smaller sensors) will not be required to have lens systems to 'get into focus' with less 'adjustment-shift (low DOF are hardest to focus; high DOF are easier to 'appear' focused even if not)

ALSO... MUCH DEPENDS...

on which system one uses to do what folks consider most technically relevant to photography apart from the specific equipment controls themselves, and that is ASSESS LIGHT CONDITIONS, and how it impacts the intended 'LOOK' of the image when it is captured... one can do it the SLOW (old) way, like one did in the FILM days, or one can do it the FAST/INSTANTLY (new) DIGITAL way... which do you prefer? I prefer the latter over the former.

Nikon has been SLOW to adopt the faster digital ways to assess light, and allow its shooters to control/adjust its cameras for EXPOSURE DETERMINATION, except allow/offer it in their most advanced PRO BODIES (D3 series only, and now D4 partially?) and even now, very late, consumer D800 partially [none of the lower older D###/D#### Nikon dSLRs have it]. This is why Nikoners still have issues/discuss exposure issues getting it wrong; or 'former Nikoners' using 'old methods' on newer Canons (ignoring/bypassing/underutilizing) what Canons can do the newer faster way.

Canon has been LEADERS in INVENTING the faster digital ways to assess light, and allow its shooters to control/adjust its cameras for EXPOSURE DETERMINATION (Sony only FOLLOWS; because they do NOT control the patents for this; and use it in LIMITED MODELS not across the board like Canon does/can). For those who actually KNOW that the newer/faster method is available, both utilize and master it; those who do not, still using older methods above, will continue to have/discuss issues related to EXPOSURE when there should be NONE. Canon has been offering the newer/faster 'digital' approach to LIGHT ASSESSMENT since year 2000 in their PowerShots (G1/Pro1-IS), and in 2005 their 1st LV dSLR model (20Da) and every LV dSLR since 2005.

Nikon for most of their LV dSLRs, still required the photographer to ASSESS LIGHT the old way that FILM SLR photographers did, and that was resort to relying solely on TTL Light Meter Scale Reading (one dimensional value only, a point on a scale) when going through spot/area metering 'routine'

Such OLD/SLOWER FILM STYEL TTL methods (still available on Canons for the sentimental) are ridiculously slow compared to instantaneousness of FULL IMAGE light assessment the CANON digital-LV ExpSim way). Why assess a mere point (or points or area) of a LIT SCENARIO, when one can assess the ENTIRE PREVIEWED LIT SCENERY that the IMAGE SENSOR SEES (millions of pixel points covering the ENTIRE IMAGE in the LENS) in a SINGLE GLANCE? Welcome to 'digital' era LIGHT ASSESSMENT... it's been around for 12+ years on Canons (dcams and LV dSLRs together). But only 5 years on Nikons (restricted to PRO BODY D3 onwards; NONE on their lower dSLRs, except 'partially' on a few low-mid end dSLRs; NONE on ALL their dcams)

Many folks FAMILIAR with this 'digital era' LIGHT ASSESSMENT of ExpSim LV (Exposure Simulation Live (Pre)View) know Canon has the best 'least hindered', 'least crippled/compromised' implementations of this CAPABILITY (most likely they hold FULL control over it).

Canon allows minor competitors with limited models this limited capability:

Pentax Optios (some/partially); not Pentax dSLRs nor MF
Olympus 43d (2008)/m43 (some/partially/fully/weak indirect controls), not Olympus dcams
Panasonic 43d/m43 (some/partially/fully/weak indirect controls), not Panasonic dcams except LX series (part-time only)

Sony is the only other mfr offering it more fully earlier, but very limited adjustments (speed/aperture/ISO); their 2005 (7 years ago) DSC-R1 was a perfect example of a model allowed the widest range of adjustments (older/later models were crippled with subset adjustments). Sony is able to do it more than other simply because they've been LONG COOPERATIVE partners with Canon (especially earlier years when making sensors spec'd by Canon for Canon dcams; not EOS LV dSLRs)

Fujifilm (nada; zilch; none; no models have it; even now)
CASIO (nada; zilch; none; no models ever have it)
KODAK (nada; zilch; none; no models ever have it)
Other mfrs 'behind' are allowed it (Samsung)

Thus Canons history for full (menuless) control/full-time 'exposure simulation' live (pre)view started with their PowerShot G series, and followed w/ LV dSLRs afterwards:

2000+ onwards: PowerShot G series; and others A/SX/S (but not lower 'easy-auto' models)

2005+ onwards: ALL EOS LV dSLRs with ExpSim LV:
20Da (2005 for astro-only)[APS-C; 1st dSLR EVER with ExpSim LV (limited to astro-only)]
1DMkIII (early 2007 fully/full time)[APS=H; 1st dSLR EVER with full time ExpSim LV]
1DsMkIII (2007 fully/full time)[FF; First FF ExpSim LV model ever, but in PRO BODY ONLY]
40D (2007 fully/full time)[APS-C]
5DMkII (2008 fully/full time)[FF; First FF ExpSim LV in Consumer/Prosumer Body; 1080p ExpSim LV; 1st ExpSim LV VIDEO EVER in a dSLR]

Where was NIKON all these years? NOWHERE. NONE had ExpSim LV at all, with their LV. They were ASSESSING LIGHT the 'ye ol' fashioned FILM SLR TTL light meter spot/area metering with NON-IMAGE SENSOR light sensors on their LV dSLRs.

MOST of their models had the LESSER simple non-ExpSim LV 'framing/focus' AUTOGAIN type of LV... till they finally offered it exclusively for their PRO-BODY ONLY top end dSLRs (even with less effective controls; none of their controls being Canon EOS-1 based (which is FASTER/FASTEST more/most effective)).

If you are a Nikoner, and confined to ASSESSING LIGHT the TTL-way (no choice; lack ExpSim LV),
or
You can be a Canonite, and ASSESS LIGHT the Nikon-Old-Film-TTL-way (be stubborn, slower by choice; or oblivious to your options to do it even faster than you already know mastered how the old way),
or
If you are a Canonite, and ASSESS LIGHT the Canon ExpSim LV way (faster; utilize its capability)...

by the time any TTL-ASSESSOR has done more than a single light assessment (aka: 'meter reading routine), the ExpSim LV ASSESSOR will have already been getting of perfectly chosen SHOTS 'first time right' shooting 100% in OVF even in Full M/M ISO!!!! [zero chimping; zero histogram consultation; zero need to ETTL chimp at all]... [which is a 'norm' for 'exposure-sim' LV savvy PowerShot G+ shooters for the last 12+ years...]

[memorizing exposure settings notwithstanding; because this applies to anyone with experience; that is, no light meter assessments at all, but shoot with presets used before even turning on the camera]

once one masters ExpSim LV of dSLRs (or ES-LV of dcams), one never wants to go back to TTL light metering ever again (it being inherently a slower LESS PRECISE/LESS PREDICTABLE/LESS RELIABLE process)... thus, why bother with a Nikon, unless it has ExpSim LV? (why opt to handicap oneself with a slower limited tool (Nikon) when one can opt for the fastest possible (Canon)?)