Before Github, there was no collection of open source repositories that are easily searchable, making it easy to find and promote open source software. I am not aware of any alternative that ever did or does a better job at making open source contributions that easy. Even when I try to use codeberg as an alternative, my Github repos will always get more contributions. No idea how we could even begin to change that.
Drew DeVault on the biggest threats to FOSS and some proposed solutions (fosstodon.org)