If I may add another caveat to that list: Pressure and standards.
A key component of the success of an Avengers approach to franchises, is for the component films to all be good, or at least not embarrassing disasters. Iron Man, Captain America, and Thor were all well-regarded and successful, and The Incredible Hulk ... wasn't the other Hulk film. Since Hulk had been first, they had time to release a new version that retconned it into oblivion, but imagine if it hadn't been. Or imagine if DC were in the middle of trying to set up a Justice League film franchise when last year's Green Lantern came out. Would they be stuck claiming that was canon to an otherwise good series? Would they have to order a do-over and lose precious time they were planning to spend making and promoting another character's intro film?
And it gets thornier the more heavily invested the studio is in the idea. The Avengers, I assume, wasn't officially greenlit or maybe even planned until the series of films that lead into it was well under way. So if something had gone horribly wrong before that point, there'd be nothing really lost as far as anyone would be aware. But any future attempt at cashing in on that model would be planned out from the beginning and probably heavily invested in.
A key component of the success of an Avengers approach to franchises, is for the component films to all be good, or at least not embarrassing disasters. Iron Man, Captain America, and Thor were all well-regarded and successful, and The Incredible Hulk ... wasn't the other Hulk film. Since Hulk had been first, they had time to release a new version that retconned it into oblivion, but imagine if it hadn't been. Or imagine if DC were in the middle of trying to set up a Justice League film franchise when last year's Green Lantern came out. Would they be stuck claiming that was canon to an otherwise good series? Would they have to order a do-over and lose precious time they were planning to spend making and promoting another character's intro film?
And it gets thornier the more heavily invested the studio is in the idea. The Avengers, I assume, wasn't officially greenlit or maybe even planned until the series of films that lead into it was well under way. So if something had gone horribly wrong before that point, there'd be nothing really lost as far as anyone would be aware. But any future attempt at cashing in on that model would be planned out from the beginning and probably heavily invested in.