Well, Pirates of the Caribbean has been a Disneyland staple attraction since the 1950's, so they've got nearly 50 years of data to go on, on whether they should continue it or not - it's exactly why they made the first film.
When you consider how much the first film made, given it's actual cost (and the acclaim Depp got for his character) - the 2nd and 3rd weren't really that much of a gamble, but one that ultimately paid off.
The film industry isn't entirely an exact science, WALL-E for example had an entirely different ending which Pixar redid after it's first screening, after Andrew Stanton realised he had made an error in the way the story flows.
You also have major blunders - Waterworld anyone? It cost nearly double the budget that was set aside for it and it's gross revenue was barely more than that. The budget doesn't take into account the marketing costs, so money was lost on that film.
That's my point. A big-budget film is a big risk. Film studios wouldn't take on the added risk of two or more big-budget movies at once without a good reason. The benefit is that it saves money in production, so they do it when the financial success of the sequel(s) is close to a sure thing.
When you consider how much the first film made, given it's actual cost (and the acclaim Depp got for his character) - the 2nd and 3rd weren't really that much of a gamble, but one that ultimately paid off.
The film industry isn't entirely an exact science, WALL-E for example had an entirely different ending which Pixar redid after it's first screening, after Andrew Stanton realised he had made an error in the way the story flows.
You also have major blunders - Waterworld anyone? It cost nearly double the budget that was set aside for it and it's gross revenue was barely more than that. The budget doesn't take into account the marketing costs, so money was lost on that film.