i think to some extent it's a lil unfair to think of youtubers (or anyone that makes stuff) in these terms. truth is people change, including viewers, and you aren't going to continue resonating with what a creator makes forever, and they aren't gonna resonate with their old content half a decade down the line either. it'll feel stale because you're used to it if it's never changed, and if they change it you might fall out cus you're just not as into it anyway.
there have been tons of artists and youtubers that i've thought of as my "Big Favorites" and then even a few months down the line my interests or theirs have evolved and i just don't feel the same way any more. sad but just how things go. i think that youtube's also kinda made things harder for some people, accommodating Advertiser Friendliness tends to work more destructively toward creative freedom and quality than constructively
the entire "science" genre in youtube has stagnated
thats because theres no more science. you have learned it all and have become more powerful than they ever will be