I am guessing many uploaders just don't realize that yet.

On the same topic, who determines the '10 minute' and '8 minute' time scale perfect for engagement and how did they end up with these numbers?

It's the minimum length of time a video must be in order to enable mid-roll ads.

The 10 minutes one seems pretty arbitrary, but to arrive at 8 mins I suspect that Google studies how much time there needs to be so that mid-roll ads don't negatively affect engagement.

(Shout-out to all the wonderful, brilliant engineers working on figuring out how to minimize the user's reaction to cramming AS MANY ADS as possible down their brain)

extremely recently, like a week ago or so, and this video was from 3 days ago; for the next few weeks I'm still going to look at the 10 min timestamp as more telling than an 8 min one (though I'm sure youtubers will "migrate").

Looking at the channel, 3 of its videos are between 10:04 and 10:09 long. Of course, that's nothing compared to a lot of other long-form youtubers I've seen with like 80% of their videos around that timestamp.