Retrieving all types that implement an interface result differ between Covariant and Coinvariant interfaces

I'm trying to get all types that implement a certain interface but it doesn't work when the Interface is co-invariant.

This is what I'm trying:

public class BaseWidgetViewModel {}
public class Widget {}

public interface IWidgetUpdated<in TViewModel> where TViewModel : BaseWidgetViewModel, new()
{
   Widget UpdateFromViewModel(BaseWidgetViewModel viewModel);
}

public abstract class TestBaseCcWidget<TViewModel> : IWidgetUpdated<TViewModel> where TViewModel : BaseWidgetViewModel, new()
{
   public abstract Widget UpdateFromViewModel(BaseWidgetViewModel viewModel);
}

void Main()
{
    Console.WriteLine(
        AppDomain.CurrentDomain.GetAssemblies()
        .SelectMany(s => s.GetTypes())
        .Where(p => typeof(IWidgetUpdated<BaseWidgetViewModel>).IsAssignableFrom(p)).ToList().Count()
        );

}

This will return 0 but when I change the interface to IWidgetUpdated<out TViewModel> then I get a result of 2.

What am I doing wrong?