My experience of the approach configuration stall scenario is that the rate of decrease of airspeed is initially quite slow from 220kts down to 160kts, then as gear and flap are lowered, the airspeed drops off at a much higher rate and if the rate of airspeed reduction is not arrested before Vref, then everything happens very quickly.
Assuming that nothing has been done to arrest the rate of decrease of speed, then the question should be "why are the crew not monitoring the airspeed?".
Well there are plenty of distractions during the final few miles on the approach such as ATC transmissions, other traffic, configuring the aircraft, running the landing checklist, preceding aircraft separation, especially if the approach has an element of high energy, etc.
Poor situational awareness leads to overload and a breakdown in the scan, with possibly one crewmember running the landing checklist which may reduce the ability to monitor the pilot flying and the instruments.
Add in some presson-itis and life gets quite difficult.
It is difficult to recognise the onset of crew overload and there is no "pilot overload" warning lamp on the panel to alert us.
I was told by a very good TC that if you can't remember the wind direction and speed given with the landing clearance, then you're overloaded.
Manual handling is important, but it should be stressed that manual flying will not necessarily reduce overload and nor will it increase situational awareness since the workload on the pilot monitoring will normally increase.
Experience helps, since it will aid recognition of a crew overload situation developing and allow time to reduce the workload and regain situational awareness.
Gliding skills? Naaah.