In my personal observations of the matter it is more that it's just a different kind of celebrity than their original draw. Nobody earnestly cares if some hollywood star becomes a professional golfer, singer, or race car driver. They have to build themselves up anew to this new audience who is selecting 'celebrity status' by a different set of rules and criteria. Now if someone in hollywood moves to another position within hollywood like actor to director hey are still closely related to the same rules of selection so they get a boost just from qualifying to what the audience is looking at.
Given that this is where there is just a separate group of people that understands or learns the selection criteria for YouTube/Twitter/TikTok/Twitch whatever and can have more synergy transferring between these outlets. It makes sense that someone who in another setting is popular just seems to land flat when they are having to relearn a new way of presenting themselves and the old tools don't work. Even celebrities that start a YouTube channel that I at least followed in passing end up feeling terrible, and I don't think I've seen a hollywood grade external star stick with their YouTube content long enough to actually start learning what needs to change.
Given that this is where there is just a separate group of people that understands or learns the selection criteria for YouTube/Twitter/TikTok/Twitch whatever and can have more synergy transferring between these outlets. It makes sense that someone who in another setting is popular just seems to land flat when they are having to relearn a new way of presenting themselves and the old tools don't work. Even celebrities that start a YouTube channel that I at least followed in passing end up feeling terrible, and I don't think I've seen a hollywood grade external star stick with their YouTube content long enough to actually start learning what needs to change.