Del Piero has been told he won't be offered a new deal by Juve at the end of the season.
"It doesn't surprise me," Materazzi told Sky Sport Italia. "Gratitude in football has been dead for years.
"Alex could spend 20 years with the same shirt, an historic achievement, but Juventus' directors have been clear and Del Piero is not stupid.
"I'm still with Alex though."