1. Customer support
2. Certifications
3. Vendor support
I don't know another distribution of Linux that provides all these things to the extent Red Hat does. You don't use Red Hat because you want to, you use it because it's the only choice.Any business could do exactly the same thing, and do it better than Red Hat. But there's really not much reason for a customer to move away from Red Hat if they're already on it, and it would take you a hell of a long time and a dumptruck full of capital to match them on the above.
Open Core is not a business model, just like Open Source isn't a business model. A business model is promising to fix a customer's problem, certify their software, and get vendors to support them. That alone will get you a yearly renewing contract for a couple million that you then upsell over time.