I could get roasted for saying this, but the last time I said it, it immediately got sidetracked into a pit bull battle so I escaped unburnt.
I had wild Betta splendens from Laos, caught by a good friend. They bred in a 30 inch tank, and the fry grew into adults with the parents, who never had to be separated. I looked at my friend's go-pro footage from the habitat, and created something like it. The males, who as wilds had never been linebred to fight, sparred a little, flared some fins, etc. No one got hurt. The breeding isn't just for the fins - it was for behaviour and gambling on fights long before pretty Bettas caught on. Betta splendens was the Siamese Fighting Fish when it was introduced, after all.
Jarring Bettas is driven by us as consumers. We want Bettas with commercially viable, unragged, undamaged fins, and we pay good prices for them. Then we complain about jarring.
The thing that struck me in the go pro footage from underwater in Laos is that the Betta splendens male it focused on hovered in place, waiting for flies and love, seemingly in that order. He was one boring fish - waiting in ambush in the reedy habitat, to wallop food. Another fish appeared in the background, moving very little. It was impossible to say if it was male, but video guy seemed unconcerned. The go-pro footage visibility was well under a metre, but that's more than I expected.
So while water quality may scare us, the fish didn't swim around a lot. If it had, it would have barged into the habitats of other males, and that would probably have gotten them fighting. The wilds weren't aggressive like the cultivated battlers, but they weren't easy going either. With that behaviour, small tanks can be argued for.
My friend said she saw a lot of splendens in the flooded meadow type pond, and that every centimetre of space was claimed by a male. They were hard to catch as the surprisingly clear water was knee deep and they'd dive for cover into the soft debris.