They don't spend more money for fun. They do it because they've had experiences of many on-a-weekend projects become critical-path nightmares.
Owning your own bespoke platform is a giant money hole. The arguments in favour of doing so are plug interchangeable with "let's write our own operating system kernel / database / programming language / HTTP server / CPU architecture / web framework".
I also think it's a bit rude to assume that Red Hat has hundreds of brilliant engineers just phoning it in. I work for Pivotal and we are flat. out. every. day. writing this stuff, because it turns out that this stuff is a lot harder than it looks from the outside.
And the reason it looks easier is because we did the hard work for you.