Probably because the AOT runtime doesn't run on game consoles, straight out of the box.

Capcom has their own fork of .NET for the Playstation, for example.

I don't know what kind of GC they implemented.

They just haven't announced any plans to do so yet. They might one day.

They will not be using .NET AOT probably ever though. Unity's AOT basically supports full C# (reflection etc) while .NET opted to restrict it and lean more on generated code.