This doesn’t have anything to do with virtualization.
You just compile stuff differently.
The problem is that Epic made UE the way it makes stuff the way you’d need tools that are only available on apple computers.
Nothing prevented em to make UE to produce stuff the way it would be possible to use multiplatform tools for compilation, they just didn’t.
As a counter-example, you can build for GNU/Linux and for Android/Linux from under any OS, because all the tools necessary are available for every OS.
As for the testing, in an ideal situation you’d only need to verify your test environment once.
But UE is very far from ideal, so yeah.
Probably because of not enough degrees.