For me, it's the lack of mobile view. I like this place, more than any website I use (and I use a lot) but having to zoom in and out and move the screen with the text to read is just as painful as nails on chalkboard.
If you appreciate the knowledge one can garner from this forum, then you'll prolly not stop visiting the forum as often as you do for the reason above, I know it's pretty difficult for mobile users at first (I access this site with my mobile, and I'm currently using my phone to type this), but with time, the hassle becomes unnoticeable and you just get on with things as normal.
There is as yet no reason for me not to visit this website, except occasionally when I have a busy schedule in real life (like during exam period, family time, etc), OP, I'll suggest you either get a PC if you don't have one, or you just get used to the website on mobile till Theymos creates a mobile-friendly version.