They make sure enterprises can run Linux that doesn’t “suddenly” (read: with less than 2-3 years notice) break their critical workflows because some component loses support or some dependency reaches EOL - they do this by extended maintenance, backporting (security) patches to old versions, providing tailored support etc.
This is very valuable to enterprises and so they pay a lot for it.
For example, you can still run Red Hat 6 safely and securely until 2024; by that point Red Hat 8 will have been out for 5 years already.
Red Hat is the premier organization doing open source development. They optimize the experiences for enterprises: lots of support and a goal of helping it be easy to use so enterprises can focus on their business logic.
Lots of well-hated projects come from Red Hat: systemd, wayland, ... but they have also contributed well to some other projects which are much less controversial.
Services/products of a company usually bring one of the following to customers: 1) improve revenue, 2) lower costs or 3) manage risks. RedHat is probably mostly about the last one, manage the risks of running linux.
This is very valuable to enterprises and so they pay a lot for it.
For example, you can still run Red Hat 6 safely and securely until 2024; by that point Red Hat 8 will have been out for 5 years already.