Looking at the flight status for KIX route, it looks like everyday UA is upgrading 10-20 passengers, and the flights still leave with empty J seats. Great for those trying to upgrade but it can't be good for UA's bottom lines. Y looks fairly full so UA can't down gauge.
Which is why UA has used the 787-8/787-9/777-200ER on the route depending on the time of year. It seems to me that the 787-8, which UA might not have enough of at the moment given they only have twelve and they are the only international widebody that has relatively few seats upfront, would be better used on SFO-KIX year-round. KIX is one of those destinations that is documented to struggle to sell tickets upfront for any US airline.