Planes are designed not to have an engine failure, should we not practice forced landings too?
As said above a 150, in approach config, handled a bit roughly can drop a wing. And if it's on approach you damn well want to have recovered from it before in a training environment.
And the 3,000ft? As I said above, why go lower for initial training at least? I don't think I ever lost more than 500 ft (or even 250ft) and I don't think many people do, but there are enough stories.