Peekay4 :
The fact is, two experienced and presumably well trained pilots from a major North American airline tried to land on the taxiway. The question is: why?
your question reminds me of something I read long ago : It was something like this : : **** happens for no reason sometimes. One day you do something irrational and no-one can understand why you did it, including yourself "
Fixation , fatigue, light hypoxia, mental distractions, micro-lapses, are for instance things you cannot measure with certainty , especially a posteriori.
Maybe it is one of these, maybe not.
As someone said, the crew is available and surely will be debriefed , but I bet you lots of beers that the PF will say : "I really thought we were aligned with the runway" . An where do you go from there ?