It does, and I've even had Gitlab as the primary repo for some time. But if your projects pick up any steam, github mirrors are going to pop up whether you run them or not - I've had people mirror my projects onto github because it means less questions for them when they want to package them for their organisation or minor packaging system than pulling source from "not-Github". Of course, the license allows them to do that, and they're upfront why they're doing it, but if there's going to be a github mirror anyway, may as well have it official.

Also if we're being honest, despite Gitlab being the #2 platform, you're going to get less contributions than on Github as people just aren't going to want to sign into a second service. Now most of my public projects are like "I made this, I put it here to show off, and use it if you like" so if people _don't_ use it, it's no big deal for me, but if you're in it for revenue or clout or just like seeing usage numbers going up, it's clearly not the optimal choice.