The All Blacks went out of their way to include the injured Waisake Naholo in the squad for the tournament, leaving in-form utility Piutau on the sidelines.
Piutau told the Daily Mail that All Blacks coach Steve Hansen told him his move to Ireland was not the reason for his omission, but the former Blues back remains unconvinced.
"It's human to have those 'what ifs'," he said.
"I gave everything I could to be selected. I knew there was a possibility that moving could affect my chances.