Beyond support agreements that others are mentioning, the huge requirement for the shop I work at (mid-scale high performance computing center) it’s 3rd party vendor package support. Mellanox/nvidia, whamcloud, slurm, vast, and on and on. Driver packages targeting rhel kernels are an industry standard offering if a vendor supports linux. That’s not always the case with Debian variants, for instance.
Same with huge applications and proprietary compiler suites (think matlab and the intel compiler suite or OneAPI). These are hugely important packages for a number of shops.
Don’t get me wrong, I can build against plenty of other distros but my vendors target rhel as a first class citizen for both build scripts and straight binary packaging.