Because then the only thing you're relying on the centralized closed-source company for is actual git hosting. This is a boring problem that dozens of other services solve well, and thousands of other services (like S3) solve poorly in a pinch. If you can migrate the interesting part of GitHub -- issue tracking, PRs, wikis, etc. -- to another provider, and GitHub just holds your data, then you're no longer locked in.

If you don't build it and you wait for the centralized closed-source company to, then you're putting your project even more in their hands.

You could build the features for GitLab. We'll roll them out on GitLab.com that you can use for free. We can import repo's and issues already and are working on PR's and wiki's.

Migrating issue tracking and other stuff out of Github seems like a good idea if you want to reduce dependency, building a bot on top of Github issues - what you implied in your parent post - not so much.