Grant is like that one girlfriend (or boyfriend) you never really get over. Fans fall in love with him, he is intelligent, wellspoken and engaging in interviews, he participates in the community, and on the court is a blend of the perfect team player and a Sports Center highlight reel. Then he leaves.
In neither instance did he leave for more money - he left for "a better situation." In both cities that was interpreted to mean "your team isn't good enough for me."
In Detroit it was so poorly received because Joe Dumars had just taken over and it was thought that he and Grant were close (they lived just several houses apart) and Grant didn't give Joe a chance. Without even getting an offer from the Pistons, Grant secretly flew down to Orlando and returned with an offer he had accepted. To Grant's credit, he allowed the Pistons to negotiate a sign and trade to get Grant more money, which netted the Pistons Ben Wallace. Much bitterness ensued.
Frankly, when a player plays the system and jumps to supposedly better teams, it is fair for the jilted team to compare relative subsequent success. While the injuries should never happen to such a nice person, it is also fair to note Grant has had way more than his share. I believe it is a testament to Grant's toughness that he keeps coming back. Any other player with that much sitting in the bank would say to hell with the level of rehab required and just retire.
As for the accusation that the Pistons ruined his ankle with a misdiagnosis, that noise subsided after the second or third round of operations in Orlando. The doctor that made the claim about the Piston's diagnosis misdiagnosed the problem as well. It turned out the injury was more of an alignment issue which required reshaping the bones in the ankle. Even Grant has exonerated the Pistons; he even strongly entertained the idea of returning to the Pistons, but chose the Suns instead. The bitterness in Detroit faded with Grant's medical problems, he would have been welcomed back.