> Per-copy licensing, which is the base of most commercial software distribution, is pretty much impossible with the GPL.

Equivalent basis for support contracts, which have actually been the key part for many years in most non-consumer software contracts even when they nominally include copyright licenses, are quite possible (and common) with GPL software.

When you are selling a support contract, GPL is no problem. But this does not cover the sale of a software which costs many thousands per seat, you cannot make up lost sales revenue with support contracts. The cost pressure would drive customers to use the software with way more seats than they have support contracts for. And the GPL would prevent any legal licensing scheme which would try to enforce a support contract per user of the software. There are exceptions to this - a hosted platform like github can of course count the number of accounts created for invoicing.

Red Hat charges per server, which is pretty much the same thing as per copy licensing.

They figured it out.

You're not paying for the software on that server.

You're paying for a license to use a few non-free packages containing trademarked material (basically the visual skins / logos nicely factored out) but more importantly, support.

And the success of Red Hat comes to no small amount from other software companies, which certify their software products often on Red Hat only. That means, if you are trying to get technical support for that software, it might depend on running on red hat. Of course, the software would in principle run on most other Linux distributions, especially Fedora, but I have seen smaller incompatibilities when running not on Red Hat. So this creates a certain market pressure to use Red Hat.

RedHat is smarter than everyone. The have obtained security accreditation that is required by the USG and many commercial auditors. Ultimate lock in and profit from a protected position. How many RHEL license are bought by the USG and the Fortune 500 for only this reason? RH, the compamy, is a good citizen. These rules only become onerous if you have money, so it is accepted.

Not really. Customers are more than free to switch to CentOS, or even other distributions or pay someone to fork parts of Red Hat. Red Hat is providing support.