NW's NRT flight (that DL inherited) seemed to be pretty popular back in the day (but, much more recently than the DL PDX hub era); O&D demand was supported by feed on both ends (AS in PDX and a hub at NRT).

But, now AS feed isn't really a thing, NRT is no longer a hub, and NRT's attractiveness from an O&D standpoint has decreased markedly ever since HND became a viable option.

It's conceivable that AA, JL, NH, or UA could make PDX-HND pencil in the new environment because all four could provide connections in Japan and the former two could rely on AS in PDX, but none of them have bitten, in spite of likely subsidies from the Port of Portland and local businesses.