> imply that people are capable only of doing one thing at a time and, potentially, that they're only capable of doing one thing full stop
A lazy and overused argument. No one said only one thing can be done. Fact is time and attention are resources and by doing some thing you allocate less of them to other things.
To turn it into a specific example, in a large enough company, to make the master->main change you have to: announce it, update the repo, update the documentation, update the CI, update any automation around code, then everyone has to update their local copies. It takes time that costs the company real money. You can calculate that amount and ask the company to donate it to an organisation which can influence real change instead of renaming.
Furthermore, it's human's psychology that once you've done such "token good deeds", you feel good about yourself and less inclined to do some real thing, right now. Not everyone is subjected to that mentality, but I think most do.
A lazy and overused argument. No one said only one thing can be done. Fact is time and attention are resources and by doing some thing you allocate less of them to other things.