I think it has a lot to do with personality and genuine effort to distinguish themselves as unique. People actually did abandon top gear to go watch Grand tour in droves because the people behind it were so likable and put in so much effort, making them unique.This isn't a phenomenon exclusive to streamers. Reminder that Oprah thought all her audience would follow her to her new channel when she stopped making her show. What actually happened? They watched Ellen instead. People really overestimate how actively engaged their fanbases are.
The vast majority of streamers are talentless lazy hacks or became talentless lazy hacks as they started streaming making most of them very similar. There is very little difference between Hasan and other political/reaction streamers, just as there is very little difference between pokimane and other E-thot streamers and on and on and on with most streamer sub-groups.
The only people I think could get their audience to migrate would be someone like Jerma whose personality mixed with genuine effort created something so unique you simply can't find anything but shitty low effort copies on Twitch.