Why did they put Stan Lee into DC’s Teen Titans Go! To the Movies?
Stan Lee is the face of Marvel, and comics in a much larger sense. He's one of the most easily recognizable names of the Golden Age illustrators who are still alive. Given that Stan Lee actually receives nothing from Marvel (that "Executive Producer" credit he's always given is merely a show of respect, but they don't respect him enough to give him a dime from the profits), so the fact that he shows up in a DC movie is great for comics, and great for Stan as I'm sure he got a paycheck for it.