It’s in Simmons head. Did you not watch that pivotal game 7 game against Atlanta. Dude passed up an open lay up that could had saved the season for Philly.
If Philly was as convinced as you are that he can work out the offensive flaws he has, no way he would be offered up to every team in the league right now. Other teams are not convinced either, as they are offering up pennies on the dollar right now.
I’m aware of what his flaws are. That doesn’t change the fact that he’s been ROY, a multiple time all-star and all-NBA defender. His 16/8 career averages and ability as a finisher support that he’s a 2-way player. He’s not just a defensive specialist. He’s not Ben Wallace or Dwight Howard. Neither of those guys could handle or create for others like Simmons can.
Simmons is more like a 6-11 version of a young Jason Kidd. A stud on both ends, but not a good shooter.
As for Philly’s motivations, they’ve been outlined already. It’s nowhere as simple as you’re trying to make it. Not only that, Simmons unwillingness to return there further complicates things.
The long and short is Simmons is being made into a scapegoat for Philly’s failures when they are far from all on him. Other players have underperformed. And they haven’t exactly put the right group of players together not have they used them correctly. For example, nobody in their right mind should have Joel Embiid out on the perimeter shooting 3’s. Yet the geniuses in Philly do exactly that.
And if Simmons lack of shooting is why he’s out there, that’s on Philly for putting together an incompatible mix
Like a lot of players that finally landed in the right situation with the right team, Simmons can most certainly be part of a title team.