They can just send other people to last year. The FAQ only talks about individual guests, not companies. The only ones that can't come as a guest in an official capacity are those 5 listed.COVER didn't sponsor 2024 edition, so they need to pay for the slots.
I still think that's dumb reasoning, Hololive will pull up numbers just by existing, there's definitely better ways to bring more variety and opportunities to smaller creators.
The reason Mozu paid is because all of them were there last year with the exception of the new girl and alpha, so they had no B-Team to send instead.