The 76ers want Simmons to be the solution; they always have since Day 1 which is why they have coddled/enabled him and paid him more than he is worth.
However, Simmons has never and still does not want to be the solution. He has chosen many times during his career, of his own free will, to actively not be the solution. He refuses to shoot. He refuses to work on his game. He refuses to change his attitude and fit into the team processes.
Simmons wants to be a passenger, get paid, play the way he wants to and be able to go home afterwards with no obligation or responsibility for anything. The signs were there for many years before he got drafted, but the 76ers, like many other foolish organizations, believed they could turn his light on and be the place where he finally put it all together. They rolled the dice and it came up snake eyes unfortunately.
Simmons will never play for this incarnation of the 76ers again. Maybe years from now, if he is still in the league, they can mend fences and he can retire as a 76er, but right now it is beyond repair.