C# List: why you cannot do `List foo = new List();`

Question

If you have an Interface IFoo and a class Bar : IFoo, why can you do the following:

List foo = new List();          


        

Answer 1

I used some linq to make the conversion easier

List bar = new List();
bar.add(new Bar());

List foo = bar.Select(x => (IFoo)x).ToList();

It is a little less versbose than other answers but works well