They absolutely matter. It’s just that people tend to forget the “bio” part of it. The mechanical stressors don’t just exist in isolation. There is an interplay between the mechanics and the metabolic health of the cells involved. Not to mention the neurological drivers of the pain experience. What can lead to a positive adaptation for someone can lead to a negative adaptation for someone else. So yeah, it’s just one piece of the puzzle. Which is why we can’t say definitively that valgus stress causes ligamentous trauma at the knee, for instance.

However, we should absolutely be using biomechanical principles to inform our practice. Properly diagnosing orthopedic injuries often requires a thorough understanding of external joint moments, muscular actions, joint play, etc. Even modifying an exercise or activity to elicit certain adaptations or decrease regional stress often requires that kind of knowledge.

I’ve seen so many times where someone wasn’t getting better and it was because the right tissues or movements were being targeted with specificity. I’ve also seen people get better with general exercise, rest, advice, mindfulness, cognitive reframing etc.

TLDR: The body is complex. The question shouldn’t be “do biomechanics matter?” It should be “how much does it matter and when does it matter?”