Probably the lost ad revenue. No company wants to advertise on those streams. By breaking them out in way where advertisers could opt out of that stream category, suggestive streamers (a huge segment of traffic) would lose money for Twitch.
Does anyone know why this is? Is it just a legacy generation thing?
If it was me hell yeah I'd be advertising on 30k viewer streams full of people eager and willing to throw money around (assume market fit, obviously)