"It would have been good to go, I was looking forward to watching him play his first game [but it's] not up to me.
"I don't know who the boss is there but they pulled the pin. It's weird."
The former Kangaroos and NSW State of Origin star has enjoyed squaring off against Williams over the past two years after the World Cup-winning All Black returned to league in 2013 following his initial five-year stint in rugby.
Williams was suspended for two NRL matches that season while playing for the Sydney Roosters, after hitting Mason with a brutal shoulder charge during a fiery NRL encounter against the Newcastle Knights, but there are no hard feelings between the pair.
"We go hard on the field and then off the field we just cruise around," Mason said. "He does his own thing, I do my own thing.
"It was great to see him come back to league and prove everybody wrong and obviously coming back to union to win another World Cup which is great for him.
"People have got to start respecting him more as an athlete. He's a boxer, union, league, what he's done in the last three years is phenomenal.
"At the end of the day they'll look at him as one of the greats in probably both codes."