I'm not talking about "normal users", I'm talking about big organizations with software engineering staff. Apple, Google, Facebook, IBM, Oracle, etc. come to mind, but of course, there are many others (incl. the peeps I work for) who have the engineering ability to contribute to or modify FOSS software in their own self-interest. And do.
Also there are many companies (eg. Red Hat) that will gladly take your money to add features to FOSS software, and they have wide expertise in doing that sort of thing.