Git has been successful despite the UI, not because of it.

Can you substantiate your opinion?

It's open source, so why hasn't an alternate interface taken over?

Because standardization matters and the first thing to become the standard is extremely difficult to unseat.

But some of types of things have in fact changed, sometimes for seemingly trivial reasons.

For example, the master/main branch shift. Everything broke when that change was made, but it happened and it wasn't a big deal.

I'm not seeing the difficulty here. It seems that a more reasonable interpretation is that git has the type of interface that is hard to learn, but intuitive once learned.

The master/main shift was fueled by political correctness. If “master” wasn't a synonym of a word associated with slavery, it would've never happened.

I'm not sure this makes sense. Are we talking the core CLI, or about any of the dozen UI clients?

For CLI, it's easy to create any number of command aliases and scriptlets to have the exact UI you want..