Matchups, irelias pickrate went down a bit for example while shen's went up, and now gues who's good vs kennen and who's not.
But mostly because people now rush protobelt and delay the zhonya's, which in combination with the ult buffs he recived some patches ago is pretty huge on him. That instant repositioining with ult on prettymuch makes sure he can always get the full ult off on the important targets in a fight, leading to alot aoe cc and damage. Also, the aditional burst from protobelt is not to be underestimated, especially 1v1.
And zohnya's also isn't that hot on him, he doesn't need the statsis cause he wants to move duering his ult and his opponents are usually stunned for the majority of the duration anyway, and the stats it gives are just poor, so people no longer rushing it helps his winrate aswell.
Honestly though, Protobelt is broken on any champ that synergies well with it. The active does stupid amounts of damage if you use it at the right distance.
Each hit beyond the first adds another 30( +07% AP) to the 150 ( +35% AP) of the first, with 8 missles total.
If you end the dash right on top of your opponent, all 8 missles hit for a total of 360 (+84% AP), and even if you end a bit infront of the target, it's still ~6 missles, so ~300 ( +70% AP).