They have plans to upgrade C# and .NET, once they complete IL2CPP: https://www.youtube.com/watch?v=Bfa9ILwlsFw&list=PLX2vGYjWbI...
Unity started as a Mac engine and only got big when they integrated C# into their tooling. Now that they are everywhere in the indie scene, why bother paying the guys that helped them get famous?
"Thank you Xamarin and bye"
EDIT: Provide some more context.