First of all, in the movie business nothing can really be pre-calculated. And nobody sets out to spend too much money. Just the opposite.
But the costs for making a movie are constantly rising, and there is no unity of vision on any project of this magnitude. There are always many, many conflicting views, and the most difficult thing is to steer these into the most coherent direction one can.
And that is even before the shooting starts, with all its variables that determine constant reactions and changes.
If it were possible, believe me, the studios would find a way to make a film without risking all these elements.
The wonder that it actually was possible for over 50 years now to continually deliver a Bond film can only be attributed to EON. They know how to handle these highly complicated productions and steer them through the harshest conditions.
And writing a great Bond script, obviously, is also the most difficult task. Hell, writing any great script is tremendously difficult, even for the masters of the craft. If you get a firm deadline for a release date, it gets even more nightmarish. Especially if it´s not just the creative people who weigh in but also the numbercrunchers and marketing people. Those now have the deciding input before approving a script.
Also, let me state once again, that nobody will cry about the grosses. In fact, EON/SONY will be happy that SPECTRE did so well.
But they nevertheless will have to answer to the moneymen who don´t really care about the product or how all these things are cyclical or how this or that factor made it more difficult to gross more.
They will point towards their predictions and the reality, measure the difference and state: we expected more. Next time, we need more.
If you want to call someone incompetent or idiotic, feel free to address those people.