Plath's all-three-games Queensland State of Origin debut did not earn him a place in Australia's 23-man squad.
The 25-year-old Dolphins utility made 21 NRL appearances, scoring four tries and averaging 86 running metres per game.
He also recorded 40 tackle breaks and 94 per cent tackle efficiency.
After starting the season at hooker, Plath moved into a bench utility role before finishing in the starting second row.
Coach Kevin Walters selected North Queensland forward Reuben Cotter instead, pointing to his experience, Cowboys form and previous Ashes tour and Origin performances.
"Max is not injured but I just felt Reuben Cotter has been there a few years now and he did a great job on the Ashes tour," Walters said.
Cotter is set for his second World Cup with the Kangaroos and 13th appearance in the green and gold.
Walters said Plath remains on course for selection: "I could have easily chosen 30 players, but Max is on the right path to playing for Australia."