How is it that the other teams have to play in play-ins while FNATIC and somehow Karmine Corp don't have to?
It's not particularly hard to understand if you look at it only from a financial perspective, directly inviting teams with big fanbases is strategic by Red Bull. KC, FNC and G2 are established names and a lot of people want to watch them, so in a way this just secures they 100% get a chance to watch, and having a big audience you can market a product to = potential profit.
For people confused just look at past HG
they always invite a couple regional teams and then hold quals/cross region invites to fill the other slots
https://www.vlr.gg/event/1752/red-bull-home-ground-4
https://www.vlr.gg/event/1169/red-bull-home-ground-3