Too small of an audience target. Add the fact they never attracted major investors meant they were doomed from the start.
Kick and Bilibili are still viable alternatives to youtube and twitch (niconico is poorly optimized for personal streaming, if ever) if you want to stream in an unfamiliar enviroment.
And before you ask, no, hololive isn't banned on bilibili, they've been Streaming HoloFes5 at the same price as other sites.