Sure, git is a commodity service, just like text editors are a commodity product. It's trivially easy to migrate a Git repository to a different service, but quite a bit less trivial to migrate all of the issues, integrations, hooks, wikis, CI services, etc.
When you look at the big picture, there are much fewer players doing exactly what GitHub does.
Git ~ Text Editor
GitHub ~ Microsoft Word
Sure, git is a commodity service, just like text editors are a commodity product. It's trivially easy to migrate a Git repository to a different service, but quite a bit less trivial to migrate all of the issues, integrations, hooks, wikis, CI services, etc.
When you look at the big picture, there are much fewer players doing exactly what GitHub does.