Think about it. If you're a Mac user, would you work for a startup that says " This is a pure .NET shop and proud of it! You won't find any of those Apple hipsters here!"? If not, why do you assume the opposite is somehow very attractive?
It's like saying a Windows user wouldn't want to work at a Node.js shop. What does the dev tech have to do with the OS? And yes, it's a fair comparison, especially since Xamarin.