He's the most popular champion in the game. That means that even if he's really annoying to face or is fundamentally broken, he will never get a real rework. The guy is literally on every LoL ad, frontpage, merchandise etc.
Being the bringer of $$$ gives you rework immunity.
Also, if you're new around here, this is Riot's priority list:
2. Chinese market (see 1.)
3. eSports balance
4. Prestige skins (see 1.)
5. Actual balance