There may be three things going on
1) No advanced seat assignments for people booking through travel agencies, etc
2) Flight times might not be particularly convenient
3) Not a whole lot of HND traffic - as NRT would be the likely connection choice
Wit that, my run to HND was a pleasant surprise due to cabin loads. I had sets of three seats both ways, bulkhead (unfortunately, could not lay across) and a regular EC row - and I slept all the way. It was a great, great flight
if you can get yourself on a row of four in the middle, you're golden!