Yeah no, this one is very Apple-specific. Just google "windows 10 vm image" and see what comes up. Obviously with Linux distros, getting images isn't a problem either.
I'm sure there's some dumb shit that MS does too, but Apple is completely alone in not even giving you any way to run their OS in a VM for development purposes.
As others have pointed out, those official MS VMs are for evaluation only. You are not legally allowed to use them for development. Of course, you could pay MS for a license and do your Windows development in a VM on Linux (or Mac), so that is something that MS supports that Apple doesn't. But to develop for Windows or Mac/iOS you will most likely need to give some money to MS or Apple.
This was non-commercial and there wasn't any development involved. Even if doing this in a Windows VM technically violated some license, I wouldn't care much for something that's just a hobby project.
As you pointed out, with Windows there's at least no technical barrier to running it in the VM. Even if I had to buy a license, that would be like a hundred times cheaper than buying a Mac.
I'm sure there's some dumb shit that MS does too, but Apple is completely alone in not even giving you any way to run their OS in a VM for development purposes.