In a word........Jealousy.
MJ was THE NEXT BIG THING going in 1985, Thomas saw it and it led to Isiah leading a freeze out of MJ during the ASG that year.
IT was also jealous that his city, Chicago, took to MJ---a NY kid---over him.
After battling through the Bird's Celtics and Magic's Lakers to get to the top, he saw the Piston's would be dynasty coming crashing down at the hands of a rising MJ and the Bulls. The Pistons were never the same after the series. And their babies pouting as they were leaving the floor before the game/series was over.
IMO, the Pistons were straight up punks. But I will give them credit for pushing MJ to get into the weight room. Because of the Pistons, MJ became THE ruthless superstar, the GOAT. MJ might have a punk, as someone says in this thread---which is an opinion not fact, but IT and Laimbeer were classless jerks who deserves every negative thing to happen to him, especially IT during his NYK GM tenure.
Good riddance to the Pistons "Bad Boys."