I switched to trail and found I stopped getting injuries related to lateral stabilization of my hips and legs.

I've come to think it's because the trails challenge those stabilizers sufficiently so they get trained properly rather than... I don't know, repeatedly being irritated by running too straight for long periods of time?

I'm not a kinesiologist so I have no idea what the real difference is, but I do know I get hurt far less on the trails than I did on pavement.

One possibility is that I go slower overall so I can't push the limits of some muscle and tendon groups like I could on pavement. Everything gets more equally pressured, but less on average.

Interesting, as if a narrow kind of stimulus is detrimental to biomechanics, while diverse terrain, even if more challenging, keeps each angle of motion hit below the limit

I've thought the same thing. I always feel more balanced when including the challenge of uneven terrain. When I was a kid I used to be able to run full speed through forrest litter.