I've been trying out different Linux distributions when I came across Red Hat's Enterprise Linux (RHEL). I then started wondering how Red Hat gets money from the product. The Linux kernel is GPL which means people who buy RHEL can get the source code and make it completely open source too. Then why do people buy RHEL? Is there some kind of loophole I'm missing?
The business of RedHat and other linux companies usually lies in selling service, training and convenience around it.
While the software itself is open source (at least most of it), they do sell the service to provide expedite security fixes. In particular they offer you the guarantee that you can run the product for at least a decade on the same software which will continue to get security fixes - something you don't get for free. They provide cloud and workplace administration services and tools to that end (those are not all open source iirc); there are integration services to bring together different existing solution to form a solution to your problems. They provide services in a form that you can roll-out your company-specific software to all workplaces in an easy way, they provide training. They provide customer-specific solutions, thus adoption of software to your specific needs and configuration / setup services - or offer you all the software as a SaaS solution so that you don't have to deal with any of the setup stuff on-site at all.
Of course, you can do all this yourself - it's nearly everything open source, RHEL without the branding is mostly equivalent with CentOS. That includes also the long - term updates and fixes for the distribution. But if your business depends on it, time is money and it still might be cheaper to pay one to setup stuff and provide the glue between different software programmes to fit your needs than figuring out all loose ends when tailoring your software setup to your needs.