Github/gitlab is miles ahead of anything you can get with Perforce. People are not just pushing for git because they ux of it, they're pushing git so they can use the ecosystem.
There’s nothing technically worse about perforce with regard to CI/CD, if that’s what you’re talking about, except that of course there are more options for git where you just click a button and enter your credentials and away you go. But that’s more a function of the fact that there aren’t as many options for perforce hosting and companies are more likely to host it internally themselves.
If companies are using perforce but aren’t running any CI/CD that’s because they’re lazy/small/don’t see the value.
Swarm feels like a minimal effort to me and just isn't as frictionless as GitHub. Id rather have Swarm than not, but it's not great.