That's a good observation, the energy is gone, I have happy memories watching them 7-8 years ago before the malaise set in. Fwiw they seem to be aware of it and play off it on occasion, but all the gimmicks feel forced now, they don't look like they enjoy what they're doing anymore. Might be a good allegory for the film and film criticism industry as a whole.
Discussion
I think a lot of those youtubers from the period didn’t want to be youtubers. They never had the understanding of what life would be like doing it as a career, and it’s surprisingly un-fun and tiresome. But the money is good enough, and they have freedom, and after years on youtube they’ve basically burnt through all their chances of regular employment anyway, so they just keep at it.
Seems to be the cycle for those few early 2010’s channels that have stuck around. They continue the grift just to keep their fanbase on life support because it’s all they have. Newer stars getting into it FOR the youtube lifestyle maintain their enthusiasm better because they know what they’re getting into.