User blog comment:Jamie/Amazing Spider-Man 3 and 4/@comment-1895174-20130618082758/@comment-1895174-20130620074845

The problem is they won't have any character individually if they're all together. If you do six villains in one film, you either reduce them down to glorified goons (like Eric Savin and Ellen Brandt in Iron Man 3), or you spend way too much time with them to the detriment of everyone else in the film. Considering the latter happens in films with only three villains, having the hero fight six villains is a good way to overload the film with too many characters. The Avengers got away with having so many heroes by being the least villain-centric superhero movie to date. The least hero-centric Spider-Man movie sounds like a disaster.

Not to mention that they'd be paying way too much for actors whose talents are under-utilized in the film. That's a good way to ridiculously over-inflate a budget. The Amazing Spider-Man was already more expensive than The Avengers, so I couldn't imagine how crazy-expensive a Sinister Six movie would be. Never mind how budgets tend to go up with the number at the end.