Well, this is pure speculation based upon the numerous interviews I've read with the members, but here goes: because they weren't very good in concert.
Not that they weren't competent musicians, obviously, but between the screaming fans and the poor quality of their systems, they found it almost impossible to hear each other and themselves, which as any musician can tell you, doesn't make for a good time for anyone. So for them to release a video, they would want it to look good and sound good, and none of them likely did. Again, I'm guessing...

That makes sense. I forget where, but I remember reading that during or after the Rolling Stones' 1969 tour, Mick and Keith tried to convince the Beatles, who never toured after 1966, that they SHOULD tour again because sounds systems / amplification had improved drastically since 1966, but the Beatles remained dubious. They must have really had a hell of a time trying to hear each other and be heard in the mid 1960s.

Of course the best source for some of their concert footage was Ron Howard's 2016 "Eight Days a Week" which included previous unseen footage from the Hollywood Bowl. It was also supposed to include their Shea Stadium performance but this got tied up in a legal suit with the representatives of the show's promoter. I'd speculate that legal claims and quality issues may be the reason that other material has not seen the light of day.

https://nypost.com/2019/01/29/inside-the-beatles-final-live-performance-and-disastrous-collapse/

The most likely reason is that someone/corp owns them and is planning to make money off of them and, like a lot of Youtube content, they weren't supposed to be on Youtube in the first place.

Peter Jackson to Direct New Beatles Documentary Film
Trove of Let It Be studio footage handed to Lord of the Rings director
https://pitchfork.com/news/peter-jackson-to-direct-new-beatles-documentary-film/

It'll all get released right after the release of the full footage of the Atlanta Pop Festival... 😛