That's not a bad question.True, Range Finder cameras didn't photograph exactly what you saw in the Viewfinder, but were close enough for most practical purposes. And from memory, some of those Rangefinder cameras cost a lot more than many SLRs did.
So why didn't Range Finders take over the camera world, leaving SLRs to the tiny niche who needed the extra features?
Besides what you mention above, because the RF didn't "photograph exactly what you saw in the Viewfinder", especially close up, it meant that macro was not really possible. RF lenses, probably for this reason, generally had poor close-focus abilities (something people who now adapt them to EVILs regret). Macro is a fun field that appeals to many people so was one good reason to choose a DSLR over a RF.
Another area also suffering from the parallax was tele. I don't think there are much if any RF lenses above about 135mm. That's a pretty serious limitation for many.
And finally, AF is much more convenient than MF. All MF systems, also SLR ones, were marginalised by AF DSLRs.
The RF being a bit smaller and more quiet doesn't balance the drawbacks listed above for most people, so it explains the dominance of the SLRs.
. . .
This is not the place to analyse all the pros and cons of EVIL vs. DSLR but I personally think the EVIL has a lot going for it and it has more scope for improving on the points where it is weak than the more mature DSLR has.
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Just my two öre,
Erik from Sweden