Control Authority
As you slow down, you need more control deflection to achieve the same control authority.
The only way to preserve authority in positive AND negative pitch at low speed is to bring in the stabilizer, the elevators are not large enough by themselves.
If you let autotrim cut out early you will run out of nose up authority...this is great for stall recovery but will kill you in other situations.
You can't point design a control system for one specific crew screw-up scenario when doing so will endanger the aircraft in other, more probable, situations.