If people really are thinking / retaining-situational-awareness why are things like this happening?
They are not maintaining situational awareness in these types of situations. The reason is because they are not monitoring the parameter that is usually automated but for some reason is now not automated.
Why? Because it is usually so well automated that the parameter drops out of the scan to a greater or lesser extent. If you fly an aircraft with no auto throttle the airspeed is a constant high priority in your scan, after years of flying with an auto throttle it has dropped down the pecking order somewhat. If asked you would probably say that it is very high on the priority list but the reality is that unless you are of unusual design, you will not be scanning it with the same frequency as you were a few years back when you had no auto throttle.
That's what the research tells us, I'd be surprised if it wasn't right.
Firefly Bobs post about automation monitoring pilots actions is spot on. In an ideal world we never would have actively automated things like auto throttles, the automation would just sit quietly watching us and waiting for a mistake. To change now is just too hard considering the relatively low accident rates v's the cost.