Because he left him, his brother and his mother when they were tiny, had no contact with the family until his son signed professional terms with Juventus then started demanding money and tractors.
There was an interview with him on an Italian football site (think its on youtube too) where he says he owes everything to his mother and hasn't seen his dad in years.
Ah, so it's like Meghan Markle's dad then. That changes matters.