I'm not saying Marvel makes bad films. I like them just the same! But it's about the mindset and philosophy behind making those films.
Marvel throws everything at the wall to see what sticks. Some turn out well ("Iron Man", "Spider-Man", "X-Men:First Class"), others not so much...("Elektra", "Daredevil", "Ghost Rider").
DC deliberates on how to bring a film to the screen. Batman '89 was in development since after "Superman" with Chris Reeve. "Superman Returns" went through 19 years of Kevin Smith, Tim Burton, McG, and Brett Ratner before being made. "Green Lantern" was almost made with Jack Black and Robert Smigel. "Watchmen".
Granted, "Spider-Man" was in development with James Cameron, but it's like DC tries to make the circumstances perfect, whereas Marvel will make "Hulk" and takes the chance, and if it's not the success they hoped for, hey, there's always the reboot option, like what they're doing now with "Fantastic Four" and "Daredevil".