I think it's also that the economics are just different. If you're evaluating a CICD tool at a small company, you're going to find something affordable and bend your process to how it works. A mid-size company might invest a bit into customizing Jenkins hoping that it will pay off in the long run. A giant company might spend millions building a fully custom system from the ground up because gaining 1% more efficiency in developer effort or even build times makes it worth it. And more than that, they may be willing to invest in experiments knowing that some will fail because the chance of success is still worth it.
From what I have seen, the internal tooling is usually worse than what is publicly available. Often times it is only used because it was built before there was anything publically available, and now all of their tooling and workflow depend on it and they can’t easily change. Plus no one wants to rock the boat and suggest throwing out a tool that likely employs a bunch of people.
And the return of investment for the change is low plus it's an extremely hard sell for management ("we'll work 2 years to get roughly where we are now and maybe get 3 minor features plus the promise of lower maintenance in the future").
