> The comment I replied to implies "why didn't the lower castes just always change their surnames"

Not implied. I was outright asking.

> I pointed out why.

By adding a non-existent condition that doesn't follow and using it as a reason.

That's unless you're saying that if the remaining lower-caste also used these neutral names, that would cause the upper-caste that had chosen to also adopt these neutral names to return to using the upper-caste names.

What's wrong with having these neutral names be used by many of the upper-caste (as they apparently are) and also all of the lower-caste? Am I not making sense? Because that's the scenario I was asking about.