Many of us prefer using open source software to develop our open source software. GitHub is not open source.

In addition to the reasons GitHub is "bad", people may just prefer to use other hosting platforms.

Possibly nothing. However, we don't want a dependency on one hosting provider. As we see with bounty source, any system can turn.

Our bugs are in a self-hosted Bugzilla: https://bugs.documentfoundation.org/

Not all projects use Github.