The community impact of GitHub is huge: I explore GitHub projects all the time, and I'm very likely to submit a drive-by fix for a GitHub project. ...I have to be pretty invested to feel like logging into GitLab. I also do often look people on GitHub to see what they do, and if they're not there, I might not assume where else to look.

But I agree with ktpsns, git is decentralized. Feel free to use both. You open yourself up to more interaction and more safety for potential issues like service outages or data loss.