Assuming this was done in free time, for fun and posted here because it looks cool, why would you hold these expectations?

This is the kind of expectations you should have of a commercial product that you're paying for. Not of someone's random side project.

As you’ve said given it's a project done in their freetime I don’t have any expectations.

At the same time when I design a project I want to share to others (in my free-time too), I always think about making it working for the majority of the users (mobile in that case).

I do too, but usually not until I've first validated the idea is interesting to people. Not much sense in optimising the wrong thing.

It's for us geeks, not the majority :)

How users (who are non-devs) are planning to use this piece, I wonder. Also is there any well established web-native way to navigate in 3d space, that works on mobile? Personally, quake-style keyboard only navigation on my desktop works like a charm.