3. The main reason is weight, particularly with aged owners.
I guess I'm now an 'aged owner', having turned 60 last year. But the weight doesn't bother me at. The size does.
Some years ago I decided to give up carrying a shoulder bag (hurt my shoulders) in favor of a waist bag. With DX, I was well covered for range, as I put the 10.5dx, 12-24dx, 24-70f2.8 and 80-400AF-D in it with a gripped D300.
With FX, I had to swap out the 12-24 for something else, or simply rely on the 24-70 to be wide enough. I added the 14-24 and shelved the 12-24.
But the 14-24 doesn't fit in the waist bag unless I take out another (more-used) lens.
As I added more gear, I eventually had more gear than would fit in my backpack too. Suddenly the 14-24 became the odd man out there some of the time.
The problem (for me) is that I'm not much of a wide angle shooter. A wider-than-24mm lens is a specialty lens for me. It's not going to be used if it's not with me, but taking it with me means pulling another more-used lens out of a bag to make room.
After some time in this situation I decided to get the 16-35vr, mostly because I was going on a nice 3-week trip to Europe where I thought it would be bad not to have something wide with me. Since a wide lens is used sparingly in my shooting, I don't really care too much about IQ differences between the two zooms - both are good enough. I did miss the 14-16mm width at times though.
I'm interested in how people that regularly use the 14-24 carry it, particularly while traveling, and particularly in terms of what other lenses people carry with it.