Ideally something like IPNS to have a mutable ref based on (repo, pubkey, branch) to resolve a commit hash, a DHT for who has what commit hashes, and then just p2p transfers. You could still have a github or gitlab for issues and CI, but code (and maybe issues) could all be p2p like git is already designed for. Your forge could also act as a peer for code cloning, of course.

Who's we? Your company?

Otherwise there's no "we", Git is decentralized. Everyone can use whatever they want.

For us the uptime issues have been annoying but not consequential enough to justify the work / risk of moving.

I suspect even poor uptime for many services is a cosmetic problem for most users.

I think the clear reason is even with their unreliability, the cost of migrating off of GitHub for _most_ places is not worth it, and so companies don't / won't (yet)

Its hard to get lemmings to change course.