It's hard to overstate the psychology behind the github profile. As a developer, your github profile shows that you're actively developing, whether it's for open source projects or for work projects. My previously company used a private gitlab install, which meant only my open source work showed up on github. My current company uses github, which means my profile shows green all the time.

We're a small company, but the github costs are a drop in the bucket. As others have said, it'd take something truly federated, or a crazy price jump from Github, for me to consider moving. It's free for my open source projects, it's a small amount for my company, and I have a public profile I can point to whenever I'm discussing my development.