A massive number of developers already have a GitHub account and are used to the tools (how PRs are done, bugs filed, etc). There are also plug-ins for basicall

A massive number of developers already have a GitHub account and are used to the tools (how PRs are done, bugs filed, etc). There are also plug-ins for basically any piece of software you want to use with it. It just removes a ton of friction. If you go with someone else then anyone who wants to contribute to you has to sign up with them. And learn the tools. No, it’s not the biggest hurdle in the world. It’s not like they have to pay $100. But it is a hurdle. Existing contributors are likely to follow you anywhere reasonable. But it could make a real difference in getting new people.