The attacker, an unused substitute in the match, said his fellow Brazilians were the only players who put in the required effort.
Chelsea went down 1-0 in Yokohama and Piazon hit out at an "unacceptable" lack of fight shown by Rafael Benitez's team.
Speaking to Brazilian website UOL Esporte, Piazon said: "A lot of us were missing the desire to be champion.
"I think Ramires and David Luiz, the Brazilians were the ones who gave the most, and now they are sad.
"We lacked character. Nobody wanted to fight... we went into a final without the will to win, and that's unacceptable."
Piazon added that Luiz, who was in tears on the pitch after the match, was one of the few players to show any sign of disappointment.
"David was upset," he said. "I'm not surprised. He was one of the few who cared and gave what he had in the match."
Jose Paolo Guerrero fired Corinthians, who were followed by thousands of fans from South America, to the win from close range in the 69th minute.