One of the big differences between The Movies Then and The Movies Now is the major difference in the constitution of the people running the studios. People like Jack Warner and Louis B. Mayer may not have had the best tastes or the best personalities, but they had the instincts of showmen despite also being businessmen. They had a gut feeling about what worked and what didn't, and I suspect deep down inside they, too, were fans-of-a-sort.
Now cut to today, and the studios are all run by businessmen with the instincts of accountants, not showmen. By and large they don't watch movies, and they almost never watch them in theaters — which means it becomes much easier for them to greenlight things which simply don't work for an audience. Or which, when they do work, work only because they exploit the most fleeting and ephemeral aspects of what an audience gets out of a film.
I hate using a term like out of touch to describe such behavior, but it fits here: they're decoupled from the end product they actually make. Imagine the CEO of a car company never getting behind the wheel of one of his cars — and not on a test track, either, but out on the road where everyone else drives.
Something that impressed me deeply about Gary Kurtz and George Lucas working on Star Wars was how they were scratching their own itches as moviegoers. They wanted to see something like Star Wars out there, and found to their disappointment that no one had created such a thing. They had to fill that gap themselves.
What happens when the people responsible for making most of the creating happen never feel that way? They turn to focus groups and other "quant"-like mechanisms, which provide deceptively one-sided information about what you're researching. They can't tell you anything about what people really want, because the people themselves don't know that. They're not filmmakers; they're moviegoers. Lucas and Kurtz ran into this headlong when Fox told them that Star Wars was a bad title because women wouldn't go see a movie with the word "war" in the name. (I wonder if, a few billion dollars later, they retired that idea.)
It's better to rely on your instincts than a focus group, because then you are the audience. You can make the leaps of daring that no survey would point towards. But today, who does this — either for a movie, or for any other kind of entertainment that could theoretically reach millions?