I doubt we can make good assumptions about those things. The cost of operating a flight to Tokyo is way way higher than to Cancun. Also, a lot of those passenger counts for Tokyo are flown by NH so UA is only getting half of the profit from those passengers on the TPAC leg.

eta: Looking at the overall data a little more, it pops out that Tokyo must be an endpoint much more than a transit point. It's the only good reason I can think of why it's overall #3 while a huge airport like FRA, with massive lift on UA plus LH codesharing, is all the way down at #10.