They weren't filling the 744 because they charge grotesque ticket fees to NRT
while providing the worst service (outside of NW, which still uses a 742).
What is worse is that their 744s only seat 357, probably the least of any
airline (outside of some far flung exec charter), driving their Seat-mile
cost up, and driving them further into bankruptcy.
This is a keen example of what is wrong with the airline industry. Back
when airlines made money, they used smaller aircraft (DC-10, 767, L-1011) to
do the truely long, thin stuff, and 747s for the big routes (of which LAX-NRT
is certainly is). The profitable EU carriers, like BA and LH (though not
last quarter) still do this. On the thin routes (PHX, SAN, DFW, PDX...),
they use A340 or 777, and for the big routes (MIA, LAX, SFO, JFK) they use
the 744. They also offer great discount deals often, far more often than AA
or UA.