If GC & runtime is on the table, then there are many nicer languages you can use (Go, D, Swift, Kotlin). I assume that the C and C++ users who haven't switched yet are largely the "GC-hating" crowd that can't.

COM and other refcounted ones get a pass. But I'm surprised that Unreal gets away with a mark-and-sweep GC. Perhaps because it's only required for UObjects, and the rest of the codebase can still easily avoid using the GC? You can even cause use-after-free bugs on UObjects, if you want to.