affiliates had an exclusivity contract for new content e.g. you could only stream on Twitch but could upload the vod to YouTube. Earlier in the year they changed the rules slightly to allow simultaneous live streaming to mobile platforms e.g. TikTok. Seems like they’ve expanded it again now that they’ve realised exclusivity was hurting discoverability
I'm pretty Linus has said on the wan show before that they intentionally didn't partner with twitch because of this and that's why they've always simulcasted. It may have changed since though.
They did have that rule in their contract for a long time. The earlier episodes were streamed by Geek And Sundry which bargained for an exclusion, which applied to all of Geek And Sundry. Critical Role, once independent of Geek And Sundry, had to negotiate a new contract and it took around a year iirc.