The devs have to constantly maintain and update those to keep working when a site changes its design.
So if the takedown manages to stop ongoing development on ytdl then even existing copies will become mostly useless pretty quickly.
Of course the server hosting LKML or in the end Linus' mailbox are single points of failures.
Edited: as pointed-out, Fossil supports decentralized issues (but not PRs). However, Fossil is a totally different system than Git.
I think this was the most popular one: https://github.com/aaiyer/bugseverywhere
But I agree with the sibling posts, while decentralised change tracking is pretty much the original idea of git, all the project management stuff (issues, comments, membership/permissions, discoverability) are a lot harder to decentralize.
I also don't think the MPAA or whoever else would be very impressed by that if the end result is still illegal activity: If the developers are known, then they'd either have to pass on the project to someone else or risk liability, whether their project repo is centralised or not.
It's the latency that kills you, not sheer bandwidth - I can watch YouTube on Tor on a good day when Google doesn't block my exit.
More people should try Tor. It's easier than you think.