While some streamers could get direct sponsors, that option is really only available to a select few of the most popular ones, and would still deprive them of the extra income they currently get from ads served by the platform. You’d have to convince advertisers to trust that each instance is going to serve their ads fairly and not additionally host content they don’t like. A system to distribute ads between instances would be complicated enough to write in the first place; these sites have a lot of QoL updates to push before they even think about doing something like that.