@nawi GitLab is just as usable as GitHub.
Open Source Software for the most part doesn't need to have high amounts of users to. GitLab is a perfect example: when the maintainers agree to use GitLab then it will all work out.
One can have a mirror on GitHub if one really wants to be searched there.
The argument "all the users are there" is bad. If someone is unwilling to click themself a free account then they are probably unwilling to perform valuable contributions too.