It's really nowhere near 50%. I went and counted stuff based on the wikipedia list which has most games with release dates and compatibility, in 2015, 255compatible games released while 57 weren't.
Out of all of these, a lot are japanese release only and shovelware and stuff, a solid 3/4 of the incompatible games fall in that category.
It's a lot of mahjong and rythm games which I assume make extensive use of the touch screen, as well as most of 4HIT LTD games who seem to specialize in tower defenses and mahjong games.
Only a few notable titles in the incompatible list, most of which are multiplatform indie games like Nihilumbra, Organ Trail and Bit Trip.
It was more than I thought it was, but it doesn't seem to be very important stuff(assuming you have a PS4 to play the indie games on).
