I think it's because it's not perceived as a professional feature. But if hitting the wheel and pressing right a few times and up a few times is professional, then I am perplexed why someone else could prefer that when shooting with the LCD (e.g., and sure, for viewfinder shooting, perhaps that works). But for LCD shooting (and we do have an LCD screen on the back very prominently), I could so much more easily touch a part of the image when I want to set focus and get it instantly. By the time I press the wheel, I could have already touched the screen and started shooting. And the feature could easily be turned off and then Rey66 and others who don't want it can forget touch exists and be on their merry way.
My guess is that those who want it vs those who don't are those who mostly use the EVF vs those who shoot w/ the LCD (macro, video, whatever).
I shoot via the EVF 95% of the time and while i'm not opposed to touch-screen as a technology, my thumb is not long enough to reach across the back of the camera and swipe, whereas i can hold my camera as i normally would to my eye and if there was a thumb-wheel or joystick within reach of my thumb, i can adjust the focus point easily.
i think it's that simple.
initially i thought what a useless feature, but i could see for anyone shooting via the LCD that it would be useful.