It's easy to make something multi-platform, but as many lone developers on all OS's have experienced, it quickly becomes a nightmare to maintain more than one platform.

Given the ease of macOS GUI development to begin with, there are more small-time, lone developers making full GUI apps there, versus other platforms.

Other platforms have a higher barrier of entry in that regard, so the landscape is more conducive to having already started out as a team and so developing a more significant app worthy of that kind of investment.