I read all of your replies and all recount that you have read A-320 accident reports and are hung up on the fly by wire system.
If the co-pilot had difficulties with understanding what the FBW/FMS system was doing, why did he not let the Captain enter the cabin?
If I was in his seat and unable to open the door using the center console panel, I would have left the seat and opened the door.
You are using this accident to trash the A-320. It is your “punching bag.” If you must blame the airplane, then be open to accepting that if a pilot doesn't know how to operate it, it is the PILOT”S fault.
Typed in 727,757,767,747-400,777, DC-8, DC10
To answer your question: Why do people land with their gear up? Situational awareness, or lack thereof. Surely along the way you've earned an instructor rating? Have you not ever had a student in total sensory overload who ignored everything that was going on, including your instruction? I've had several. Had one just about kill me in a Navajo one night. He would not relinquish control. I thought I was going to have to punch him.