The reason why they don't do that is that you can reference variable names:

    foo = 1
    switch bar {
      // Equals the value of (existing) variable foo
      case foo: return 0
      // Catch-all, binds `foo` to whatever is in `bar`
      case let foo: return foo + 1
    }

(My syntax might be off, I've never written Swift)

To do this in Haskell, you'd have to write something like:

    foo = 1
    case bar of
      foo' | foo' == foo -> 0
      foo -> foo + 1

Because you're only able to pattern-match against literal objects (constructors or numeric/string literals).

This might be different in some other ML-like languages, or there could be GHC extensions for this, of course.