Linq - Casting IQueryable to IList returns null - WHY

IList<IMyDataInterface> list = query.ToList() as IList<IMyDataInterface>;

class Program
{
    static void Main(string[] args)
    {
        IMyFunctionalInterface myObject = new MyClass();


        //myObject.Get() returns null for some reason...
        IList<IMyDataInterface> list = myObject.Get();

        Debug.Assert(list != null, "Cast List is null");
    }
}

public interface IMyFunctionalInterface
{
    IList<IMyDataInterface> Get();
}

public class MyClass : IMyFunctionalInterface
{
    public IList<IMyDataInterface> Get()
    {
        string[] names = { "Tom", "Dick", "Harry", "Mary", "Jay" };

        var query = from n in names
                    where n.Contains("a")
                    select new MyDataClass
                    {
                        Name = n.ToString()
                    };

        //There IS data in the query result
        Debug.Assert(query != null, "result is null");
        //but the cast here makes it return null
        IList<IMyDataInterface> list = query.ToList() as IList<IMyDataInterface>;

        return list;
    }

}
public interface IMyDataInterface
{
    string Name { get; set; }
}

public class MyDataClass : IMyDataInterface
{
    public string Name { get; set; }
}

class Program
{
    static void Main(string[] args)
    {
        var names = new[] { "Tom", "Dick", "Harry", "Mary", "Jay" };

        var query = from n in names
                    select new C
                    {
                        S = n
                    };

        //There IS data in the query result
        Debug.Assert(query != null, "result is null");

        //but the conversion here makes it return null
        var list = query.ToList() as IList<I>;
        Console.WriteLine(query.ToList().GetType());

        // this assert fires.
        Debug.Assert(list != null, "Cast List is null");
    }
}

interface I
{
    string S { get; set; }
}

class C : I
{
    public string S { get; set; }
}

var list = (IList<I>)query.ToList();

var query = from n in names
            where n.Contains("a")
            select new MyDataClass
            {
              Name = n.ToString()
            } as IMyDataInterface;

IList<IMyDataInterface> list = query.ToList() as IList<IMyDataInterface>;

List<MyDataClass> tmp = query.ToList();
IList<IMyDataInterface> list = tmp as IList<IMyDataInterface>;

IList<IMyDataInterface> list = query.ToList().Cast<IMyDataInterface>();