It also has to do with licensing around the tool itself (git(1))[0]. FreeBSD is licensed under BSD-compatible licenses, and will avoid reliance on tools that are licensed in an incompatible way. The advent of git-compatible alternatives[1] with BSD/ISC licenses make the move easier.
NB: the git format itself is not licensed, so only the tooling needs to have a "correct" license.
NB: the git format itself is not licensed, so only the tooling needs to have a "correct" license.
[0] https://github.com/git/git/blob/master/COPYING is GPL2
[1] https://gameoftrees.org/