Where have you heard/read about this? I've seen cases where twitch streamers have super obvious bots watching, literally thousands of them, and Twitch did nothing.
Not generally. Specific ones may be, but so far it's always been on a case-by-case basis.
For other content, it can be seen as a loss of income for the streamer if they are demonetized due to viewbots, and for those where it isn't - it is effectively ad fraud since Twitch revenue is based on those engagement numbers