I'm not a desktop environment developer, but I can't imagine it's especially fun compared to other projects. The bigger projects (Gnome, KDE, etc) are definitely being run for instrumentalist reasons, and are supported to quite a degree by companies with a business interest in having them.
Thinking about this reminded me of a highly insightful comment by user Floegipoky[0]:
> By mimicking the Apple and Microsoft tactic of constructing vast monolithic environments and applications, you have all unwittingly been playing to their strengths, not yours. Such enormous proprietary companies can afford such brute-force strategies because they have vast financial and manpower resources to draw on.
> Projects like Gnome and Open Office become like our banking industries: vast, baroque, impossible to regulate effectively, and cripplingly expensive to maintain.
Doesn't exactly sound fun — and whose itch is being scratched by working on these?
> the Linux desktop world (and even the kernel world beneath it) has completely and utterly forgotten its roots. Unix Philosophy isn't merely a neat marketing phrase: it describes a very specific way to construct large, complex systems. Not by erecting vast imposing monoliths, ego-gratifying as that may be, but by assembling a rich ecosystem of small, simple, plug-n-play components that can be linked together in whatever arrangement best suits a given problem.