I think most of it is who he’s played for, with the 76ers and Nets being conference rivals and repeat playoff opponents. If he was going through the same thing for Denver or Utah or Portland, there would be less reveling in it on here, while if he was on the Heat or Lakers, it would be the same or worse. (I’d even add that the 76ers tanking so prominently to acquire him also feeds into the schadenfreude, like they went through all that and this is what they got out of it? Ditto to the Brooklyn super team now having to rely on him after Kyrie drove Harden away.)
Look at Fultz, who was a target of similar smirking when he was going through his issues with Philly, but once he would up in Orlando, that was about the end of it as a narrative on here.
There may be some amount of ire based on Simmons’ celebrity relationships, but again if he was in New Orleans or Charlotte, I don’t think people would draw much satisfaction from his struggles.