They already have a platform-level subscription. It's Twitch Turbo and costs ~$10/month. Removes all ads on the site. I don't think creators get any portion of it like with YouTube Premium though.
IIRC I heard years ago that Turbo "pays" the streamer for the non-watched ads which have been removed for the Turbo user, i.e. fractions of a cent, i.e. nothing. All it does is paying Twitch for doing fuck-all.
So Turbo pays the streamer the same amount per stream as the non-Turbo ad supported account? That sounds good and fair. I don't know why you would expect otherwise.
Heck, Turbo users probably watch more videos and so are better customers even at the same rate.
I'm in the US and have been subscribed to Turbo for over a year now, even though I rarely watch Twitch. I just keep my subscription so I don't have to be bothered with ads when I want to turn on a Twitch stream on my Apple TV.