1) The burden falls disproportionately on Git maintainers and on people with large amounts of dependencies to the old word which is not a good way to distribute work (across tech workers) when making changes especially since some people will not even notice the change.
2) Not everyone uses Git each day and I am certain that people who continue to use the word "master" without knowing a thing about what Git is will be viewed as racist and morally inferior. E.g. (Master of Ceremonies, Master of Arts, etc.). Explain how a tech worker can agree that "master branch" is offensive but putting that they have a "Master of Science" on their CV is fine.
3) Somewhat arbitrarily changing words with a tenuous relation to racism seems like an extremely passive aggressive, murky, and dangerous path to go down. Not only does it lay a trap for people to be accused of being racist but if this is acceptable it is inconsistent with not removing all words associated with slavery. Even words with a distant relation to slavery.