Azir has been tagged by a lot of people to be one of, if not the most difficult champion in the game to master. That said, they can't buff him. He is a champion who's kit is the epitome of broken, yet that is really only exploited and shown in competitive play. While he suffers in solo queue because of it, Riot released a champion who is literally impossible to balance in solo queue without him being 100% pick/ban in pro play. On top of that, if he were viable to the masses in solo queue, the people who have mastered him would have a ridiculous advantage, and would you really want your only way to climb the ladder being "master this champion who takes an obnoxiously long time to do so?"
I'm sure you'll all look at my match history and complain because I'm saying this as an Azir main, but I'd do the same with any champion if I had as much fun playing them as I do Azir. Azir could be completely gutted to the point of being non-existent and I'd probably still play him a lot. Yet the fact remains that he will probably never see buffs save for the last one to his ult, but that was more to fix a bug than anything if I recall.