Or are there other reasons too?
Right now, the SVN reversion number is used as the internal CB version number.
That is a blocking issue; that may be simple or hard to fix.
The number of core CB developers who do not want to switch to Git is likely the main stopping issue.
Since, I am not even a CB developer I have no idea what reasons are the ones that need fixed before moving to Git.
I did read that the last key stopping issue on the GCC project was good software to maintain the SVN history during the move to Git.
With GCC, there was unofficial mirrors and later a more official unofficial single mirror for the others to use as a base.
Tim S.