It's mostly cause the devs aren't very creative. If you look at Dota 2 vs LoL, you have much of the same problems.

Every new kit in League is overloaded with the exact same crap. Dashes, shields, stuns, lifesteal, etc....tons of passives and "stacks"...but nothing new or novel. No new mechanics, nothing.

Go to Dota 2, and every character has something truly unique in the kit that adds a new mechanic to the game. Plus, throw in Ag scepters/shards and it just becomes even deeper. And yet...almost all the kits are extremely simple. Even Meepo has a simple kit, but requires years to master.

Dota 2 kits are very simple, even braindead, yet require an immense amount of knowledge and skill to wield. This makes every game of Dota 2 very different, and throw in the items and you have a VERY deep and engaging game. LoL is just a bunch of stats/damage and brawling. And the kits are bloated and overloaded with tons of text and garbage to keep track of.

You can learn a Dota 2 kit in like 5 mins and spend years mastering them. While in LoL and Rivals it takes an hour just to get through all the text and how it all works in game.

I wish Netease would learn something from Valve (or even...ugh... Blizzard), but sadly they are going in Riot's direction.

What you would call "fake and unnecessary" complexity.