My point was more on the sponsorship rather than the transition. Even if you manage to move 20% of the audience, the sponsorship amount would be less than 20%. Most companies play it safe and allocate budget for proven marketing platforms and wouldn't be willing to put much on a new platform. So while it takes someone to switch platform and convince their audience, there wouldn't be adsense money or sponsorships with no guarantee they would even make 10% of what they used to make on YouTube. Most youtubers are after the money and if anyone is doing it as full time job, that would be an unreasonable request.