Do different "regions" really have a "general common taste"?

This has less to do with any existing general cultural preferences of the region, and more to do with how that particular product type was first introduced to the region and what it tasted like at the time. The flavor profile of an imported food, and even some native foods, tends to get set in the popular preference in the first few years it's eaten there.

For example, mayonnaise in Japan is both richer (more egg yolks) and sweeter than mayonnaise in the US. This is because, when Toichiro Nakashima manufactured the first mayonnaise in Japan in the 1920's, that's how he liked it. This makes it the "flavor profile" of mayonnaise in Japan, and if an American company were introducing a mayonnaise-based product there, they'd add extra sugar and saturated fats to it so that Japanese people wouldn't think it tasted "odd" or even "wrong".

"How can these different people with only the geographical location in common have a common "taste" in food?"

This is not odd, it is the very definition of culture. People living in a given region always tend to have similar preferences for a number of things, including food, clothing, pronunciation, and so on. It's not odd that it happens, on the contrary, it would be odd if it did happen for anything but food.

The reasons are varied, and have little to do with cooking and everything to do with social psychology - people (like most social mammals) tend to blend in with their group and to get used to what is available around them as the "norm". This has a ton of functions in human societies, which have nothing to do with actual cooking, there is scientific and popular literature on the anthropology of food habits. The point is that geographic constraints, the establishment of random choices, and some intentional engineering of food choices by ideologies and marketers have led to taste "profiles" in different regions, which have become the preference of the people in that region, and producers are of course catering to these existing tastes.

You do have a point that nowadays, globalization is reducing regional differences in everything, but it is certainly not so far progressed as to delete them altogether.