Linux

Nah @exu is right: non-IT focused companies do not have the skills or desire to reliably set up and maintain these systems. There is no benefit to them creating their own server stack based on a community distro to save a few bucks.

Smaller companies will hire MSPs to get them setup and maintain what they need. And medium to large size companies would want an enterprise solution (IE: RHEL) they can reliably integrate into their operations.

This is for a few high value reasons. Taking Red Hat as an example:

1. Standardization (IE: they can hire people with RedHat certificates and they will be a few steps ahead in ramping up to internal systems)
2. Vendor support (IE: if something critical isn't working they can get quick support from a Red Hat technician and get it resolved quickly)
3. Reliability (IE: all software is backed and tested by Red Hat and if anything breaks from a package update its on Red Hat to fix)

When lots of money is on the line companies want as many safety/contingency plans as they can get which is why RedHat makes sense.

The only companies that will roll their own solution are either very small with knowledgeable IT people (smaller startups), or MASSIVE companies that will create very custom solutions and then train their own IT operations divisions (talking like Apple, Microsoft, Amazon levels).

Not to say what Red Hat did is justified or good, because hampering the FOSS ecosystem is destructive overall, but just putting this into context.