You have a misunderstanding of what Freedesktop is. Freedesktop is just a group of desktop developers that submit standards to each other, they don't really dictate anything. For that reason it tends to self-select for developers who are actively working on desktop environments, and the standards that tend to get submitted there are things that already have some level of adoption among open source desktops. You too can submit specifications to Freedesktop but you'll probably not have much luck with getting something adopted among peers if you're not already interacting with other desktop developers on a regular basis.

"Customizability" is also not the domain of a group that like Freedesktop that publishes specifications. Their purpose is to define some baseline of standard behavior for interoperability. The customization comes from individual projects. No offense but your criticism is pretty misplaced.