I would say that hosting on a centralised service like GitHub it Gitlab also reduces friction for contributors - bug reports, code, docs - as people will usually already have an account so they can make drive by contributions.

Having to find a bug tracker, create an account, log a bug is a lot of hassle for a random library or small project. I know I've given up raising bugs for some things as I couldn't be bothered with the rigmarole of sign-up, verification, etc... On Gitlab/GitHub there is much less friction because I use both regularly and and can use them for multiple projects, large and small.