IIRC youtube enables maximum monetization on videos that are at least 10 minutes long. So you end up with a mixed bag of 10-minute videos where some are content that could've been said in a couple of sentences and been 30 seconds, that were stretched out into 10 minutes of filler, and some where the content should've been 30 minutes or more, squished down to just over 10 minutes to try not to have an intimidating video length.

You say this like their viewers don't want long videos. They do. I am one of them. So if they started doing what you suggest, I'd stop watching them.

There is no sweet spot. Different people have different preferences. Not every Youtuber needs to make 10 minute videos. Not every Youtuber needs to make hour long videos. It depends on their audience.

If you don't like hour long videos, that's fine. You're not the intended audience. Stop trying to make every content creator abide by your preferences and just look for those who already cater to your preferences.

Some channels do both since people have different tastes/levels of free time. I think it's a good strategy, though I don't know how it plays out on the money side. For example, a YouTube channel about automotive fabrication and tuning ("Gingium" in this case) will release high-detail build videos in series, then when the project is over, add a "Building a [x, e.g. Supercharged Off-road Miata] in 10 Minutes" condensed video with all the key moments.

10-15 minute videos are usually nothing more than an extended /r/todayilearned post. I'm not interested in learning some new trivia, I like it when the videos are structured and detailed in a way that makes it flow like a narrative. Although some creators (like Quinton Reviews) pad with unnecessary fluff, most of the really popylar ones (Hbomberguy, Lemino, Jenny Nicholson, Lindsay Ellis, Summoning Salt) don't.

You could argue that anything except the thesis statement is a "waste of time," but the videos are for entertainment at the end of the day.It wouldn't entertaining for someone to say "The Oof sound in Roblox was invented by Joey Kuras for a game called Messiah. Tommy Tallarico says he made it but he probably didn't." then the video ends.

What is fun is watching a long deep-dive pulling apart all the ridiculous lies and exaggerations of a fascinating narcissist like Tallarico.