I think some of them actually do put in a fucking ton of work for very little actual content...folks like Captain Disillusion as an example, puts a metric fuckton of work into his videos and it shows. But yeah I think many of them just run out of ideas or get comfort enough that they realize they can get off the grind. Look at Tom Scott or Adam Ragusea for good examples of this...both of them admitted they were working too hard, and if you look at the quality and number of videos they put out, I believe it. Both of them admitted they were probably set for a while so both of them took a step back.
It's actually a ton of work to ideate, research,write, film, edit, and market your videos. Some folks choose to do it all or mostly all themselves and they usually can't keep up with super frequent posting. Others choose instead to hire teams and then they then into managers rather than content creators (what Tom Scott wanted to avoid and why he quit). These manager types are probably the most loud about how much work "they" do, when in reality The "work" is just micromanaging their team. LTT would be a shining example of this bullshit. The most successful ones post a lot to build up a reputation and a following and then usually take a step back and slow down. Grind till you make it and then chill.
Or they do like Technology Connections or Electro Boom do and just do whatever whenever however. Those kind of channels have the most staying power I think.