Bit of a speculation. Line crews commonly encounter L/G DN on tkof or g/a, where roaring engines are the loudest. No idea what the effect will be at 260 kts (but presume noisier). Devil is the noise being constant, from after the tkof/ga - thus perhaps not triggering any alert in the cognitive system if saturated already. It's not unheard of that in the SIM crews end up with the dunlops air ventilated far longer than they wished.
Not sure if the NW wheel bay doors were closed for these guys, might be another straw if so (more silent).
The awkward part is the lower EICAS, which either:
- shows a "STATUS" screen with listed inop items incl. "L/G RETRACT", or
- with L/G DN shows the "WHEEL" page with big green triangles (well, a common sight during standard final approach thus a short-circuited brain might wash that out)
The story leaks the most around the decision not to accept the first runway. I ran the numbers for ALD.