Just to give an idea what is going on... I don't think I have any videos of my own but found some others on YouTube. Look for the broken ones though when you're out vs looking for hair on every sapling. There's something magic about the broken ones. I don't know what it means. I speculate it's when you have multiple boars competing they get a bit aggressive with the on the scent markers and saplings get hurt. The aggressive bear started breaking saplings all round my immediate camp and places I'd walk through. It was annoying because I knew it would tip off other hunters, so I'd cut off the broken part and toss them, but that only seemed to escalate things.
And you're 100% right that multiple bears hit the same ones year after year.
Anyway, these are a good watch... straddle marking:
https://www.youtube.com/watch?v=WBF__dHACu8
https://www.youtube.com/watch?v=If3VX-J0Sjk
https://www.youtube.com/watch?v=0AmTy2I1goM
Grizz breaking a small tree... not sure if it is for marking reasons or not:
https://www.youtube.com/watch?v=zwY5Pzrlsew
Unrelated, but here's a bear taking a tree down for different reasons (presumably bugs) impressive and fun to watch. I don't think this is the first go at falling big timber LOL
https://www.youtube.com/watch?v=NUHPx_cFKOc