From the point of view of 'Human Factors'
1. The first is observed when the crew says that they are comfortable at 3500 feet at 5 miles. Here the crew is getting self trapped into being committed for landing
2. Second is when they announce that they are established on ILS, which they are not. Making such announcements would put lot of pressure on the crew to somehow push through the landing.
Ego could also have been triggered here. Still, the landing could have been hacked but for the fact that the gear was missed. This resulted in irretrievable situation.
Tunnel vision and get homeitis have a role.
Such mistakes though not common do happen. Here the crew were unlucky to have additional and overlooked problem of gear.