Rather they create enterprise distributions that are made up of a number of open source projects that are (ideally) integrated into a solution. This combined with the right investment in support and training provides a product that is more compelling than "we provide a signed version of $UPSTREAM_PROJECT". I would say OEL is successful for the amount Oracle appear to invest in it (not much).
Timing helps a lot too though, in that they had a lot of success before the advent of the public cloud so are in a better position to weather the storm while they figure out a new model.
Support is something enterprise customers want, and they will sign yearly contracts to get it. In return, if/when they have a production issue, 0-day vulnerability, etc, they have someone to contact (or may have contacted them!) to help them resolve the issue. And Red Hat has experts in both support and engineering, meaning resolution can be anything from a config change to a rapidly released patch. Happy customers renew year after year.
I work for Red Hat Consulting. This is a very different beast, consulting involves selling lots of short to medium term projects with the occasional long project, then trying to optimally staff those projects. You only get revenue while consultants are on the ground. It's not surprising to me that an open source company that relies only on consulting wouldn't be sustainable.
https://aws.amazon.com/premiumsupport/pricing/
But with it you generally get very quick responses to issues, and if your bill is enough, you get a technical account manager who gets paged when you open a ticket. They handle many things, but I believe AWS Linux is in that list of many.
Having the Technical Account Manager is quite valuable.
Red Hat did a smart thing and used their open source offerings to deliver business value outside of the product space. It's an approach that most other successful OSS companies seem to have have followed.