Why is Riot always buffing Jax?

I don't understand what they are trying to do. There was a time where Jax was as banned as old Kassadin/Warwick before the nerfs; he was really powerful, even though one can argue that he wasn't THAT powerful. Still, I would like to know what Riot is trying to do with all those constant buffs that do not solve nothing.

I don't want Jax having the same problem that Vayne has; she was, directly or indirectly, constantly receiving small buffs, and the result is what we have now: Vayne is very strong and in need of nerfs.