Is there any kind of indicator in the cockpit to remind the pilot? A light? A voice (like the stall voice), that says, "Hey doofus, you're descending and close to landing, so LOWER THE GEAR!"
The human brain is a funny thing. It will convince you of things that are not there just out of habit.
"Pointing and calling" (https://en.wikipedia.org/wiki/Pointing_and_calling) appears to address this.
https://www.youtube.com/watch?v=zO5rXxJRmf4&t=5m48s
(I think this is meant to be an accurate simulation of the same type of aircraft under the same conditions.)
The current top comment in this thread also quotes the investigator report for this crash as saying
> According to the FDR and CVR recordings several warnings and alerts such as over-speed, landing gear not down and ground proximity alerts were disregarded.
So, yep. Although in the simulation, at least, this particular one is not a voice alert but is an annoying bell (with details of the reasons for the alert available elsewhere in the cockpit).
But gear up landings don't happen in a normal stable approach in nice weather. Gear up landings happen when something else is going on taking all the pilots' attention. Like in this incident they were too high, too fast and descending too quickly. That causes a lot of other warnings and distractions, so they completely didn't hear the gear warning.
The thing about flying an aircraft is while it's 90% boring monotony, takeoff, approach and landing are all extremely time sensitive operations. It's easy to become cognitively saturated or to "get behind the aircraft". You can only go forward and you're going really fast so everything has a deadline.
The best description would be like when you were learning to drive and you merged onto a highway the first time. Lots going on, can't slow down, just have to commit and try to keep up.