[Alupis]

I've never used Unity, but Unreal Engine is heavily tied into the Visual Studio (proper, not Code) workflow, including the Microsoft C++ Compiler toolchain and all 30GB+ of it's friends.

I'd suspect the same from Unity.

[FartyMcFarter]

Both engines support platforms where Visual Studio is not available, right?

[Danieru]

Unreal uses the native compiler for the target platform. Windows this is msvc. Modern consoles are all clang forks. Linux is the only exception where I think they depend on clang not gcc.

[fomine3]

nitpick: Maybe Xbox One is built by MSVC?