Quoting
Raimi
"It really was the most amicable and undramatic of breakups: It was simply that we had a deadline and I couldn't get the story to work on a level that I wanted it to work. I was very unhappy with SPIDER-MAN 3, and I wanted to make SPIDER-MAN 4 to end on a very high note, the best SPIDER-MAN of them all. But I couldn't get the script together in time, due to my own failings, and I said to Sony, 'I don't want to make a movie that is less than great, so I think we shouldn't make this picture. Go ahead with your reboot, which you've been planning anyway.' And [Sony co-chairman] Amy Pascal said, 'Thank you. Thank you for not wasting the studio's money, and I appreciate your candor.' So we left on the best of terms, both of us trying to do the best thing for fans, the good name of Spider-Man, and Sony Studios."