Changing the default name would have an impact on teachability. If you're assisting someone on learning Git, and you have to ask them to find out if their main branch is called "master" or "main", that adds complication to the learning process. They'll wonder if they have to do this every time, etc. I think it would harm the Git ecosystem for the default to be changed anywhere - including hosting companies.
-Jefferson
P.S. Sorry if that was already mentioned, this is a long thread!