To test that the pilot can actually work out what the current situation is then recover. If he can't, then he needs more training.
There may not be an outside horizon, but watching the ADI as the simmo puts you in a UA is effectively the same and makes the whole exercise a waste of time
I guess it all comes out to personal opinion. In other words there is no right answer. One could also argue that in a fair dinkum UA it is most unlikely that the pilot would just happen to have his head looking down at his knees with his eyes tightly shut. It is probable that in most of the Loss of Control accidents the pilot could see what was happening a few seconds before it developed into a UA. But for whatever reason, was unable to take prompt appropriate recovery action.
On the contrary, his eyes would have been wide open on stalks, he would be frightened fartless and maybe hands on the controls over-controlling and even turning or pushing the control column the wrong way. Read the Loss of Control in IMC accident reports - it's all there and no shortage of them. Of course, all this is speculation but the point is he sure wouldn't have his eyes wide shut when the stuff hit the fan.
That being so, what is the point in the simulator of telling the bloke to look down and shut his eyes when in real life it would never happen like that? I believe the real reason some simulator instructors do the heads down and shut the eyes caper before a UA, is a throw back to their own experience in general aviation when they had this happen to themselves when training for their initial instrument ratings under the hood in a Cessna. Rightly or wrongly they simply carried that training over to a simulator.. nothing more, nothing less. Just another myth