But then that would have the downside of falsely blocking projects that were developed in private and then just pushed to Github (or any public repo). Like I always use my own, self-hosted Forgejo for everything by default.
If it's a project you actually care about and are actively working on it'll be just as good 3 months from now.
If it's something that'll be irrelevant in 3 months why should anyone care about it?
If you develop on your own private instance and then mirror to GitHub to release it then there will be 3 months of git history in the logs.