Plus the raids get nerfed over time anyway. Like you cant compare current Raszageth with Raszageth 1-2month into the Season.
There are currently 1.6k+ Guilds that have cleared Vault. And if one cant compete on lets say world rank 300 then maybe world rank 500 is more of ones taste. And if not then maybe 700 and so on and so forth. The way the game is played differs massively from world rank to world rank
People kicked others for one daring not go full cookie cutter
People can clear the current raids with green logs and arguably even grey logs.
The issue isnt the games difficulty but the mindset of some people and that you will never be able to change (and it isnt a case just in WoW. Its a case in every game with a competitive nature)
They had to settle on a fixed size for Raids. Thats why 20man was chosen as a middle ground. Could arguably do it 17 or 15.