But they're the project leader. They're calling the shots so you use what they specify.
Most projects let you pick your editor, filesystem, distribution, etc. It would be nice to add version control to that list. That doesn't seem like it would be all that hard to do. There are already tools to migrate a repository between different version control systems and they mostly use similar concepts.
Top Ten Things Overheard At The ANSI C Draft Committee Meetings: (6) Them bats is smart; they use radar.