They are indeed, but this kind of tragic... I mean, all that skill, that knowledge, the experience - working on something which, almost by definition, very few people will be able to use (because people require lots of things from their OS + apps, so that such a project is extremely unlikely to meet all of those requirements). And even as inspiration for other developers and designers - the solo OS-developer is unlikely to spend the time elucidating their design choices and architecture, in documentation, presentations, talks etc.

And this is in contrast with the solo developer of a library or app, whose work is immediately usable by many even it's an undocumented black box... OSes are a team sport.