Well in this case why Github, GitLab, etc.. do not allow you to "star" a repo more than once?
I'm fine with stars not being significant, but it's still not good if a malicious actor can suddenly spoof hundreds of accounts and spam stars, comments and what-not.
Because that's a completely different interaction. You can still create another account and star it again.
Sure, your IP will be rate-limited (GH at least) if you script it and start hammering stars, but that's not because it wants to protect the integrity of the repo star count.
We seem to be doing OK by not caring much.