He's such a high skillcap Champion its hard to balance him. That's why.
I have a decent amount of ryze games and can play him well (he was my third most played champion last week with 9 games and an 89% winrate) so don't think I just want him gutted. What I think they're doing is trying to make his one ult be permasnare and making it so he can ult A LOT can go in for a couple snares then rinse and repeat. He probably will be substantially weaker after this patch, but maybe after that patch, they'll look into buffing him some more.
Look at it kinda like a slight rework over a bunch of patches.
This is an optimistic viewpoint but I would really rather not have Riot gut one of my favorite champions again, like they did to Rengar (but they're trying to fix what they've done) and soon to be udyr. It's annoying honestly.