That's always been a bit of a mysterious redeye to me, OZ has some similar ones from other airports, I'm not sure who uses them (in regular times). They depart and land outside of public transportation hours on both sides if I recall correctly, tourists wouldn't want them because of a half night in a hotel or wait 12 hours to check in, plus the 737 (A321 on OZ) is not a great business class experience. If you're taking these flights on business, certainly you want to sleep however much you can, but not much chance on those seats, and who wants to go start meetings after 1 1/2 hours sleep?
Interesting point you make about the lack of winglets, makes sense, the -900 came out a few years before I came to Japan, before winglets of course, and that's also when those same seats were still prevalent on the KE Intra-Asia 777 fleet.
Don't get me wrong, my overall KE experience was quite positive, just was really bummed out by the downgrade of aircraft, seat, and IFE. Flight crew are top notch. They cancelled my originally scheduled flight so I had to go 3 hours earlier and wanted to sleep... that wasn't happening in the recliners.
I really hope this COVID19 clears up soon, it's making traveling in the region unpleasant at a minimum and impossible in some cases.