Why are the Sixers so bad?

I am a die hard sixers fan, and people often credit their talent with the team's horrible record. However, on paper, their roster is actually not bad. They have Jrue Holiday, who is playing out of his mind, Andre Iguodala, a superstar, Evan Turner, Thaddeus Young, Mareese Speights, and Elton Brand. Sure its not a stacked lineup, but its no where near a bad one. Young and Speights have been very solid 15 and 8 guys, with speights coming off of the bench a lot. Brand, may not be in his prime anymore, but still has something left in the tank. What do y'all think?