I'm hesitant to put my oar in with all the vitriol spraying around this topic, but I think I can explain:
By making a show of being choosy about what one eats, one achieves two ends: first, you show that you're not so poor that you have to eat any old scrap that comes along; second, you excuse yourself from eating expensive things by claiming to not like them... even telling yourself that you don't like them.
A lot of people from certain socioeconomic classes will deride any food that is "fancy" because it makes them feel inadequate; and so they make a show to themselves and others that the fancy food is just overpriced junk that they wouldn't touch if they were starving. You do this for enough generations, and you come up with a cultural behavior. Eventually the fanciness of the food is no longer the reason they don't like it, it's simply a cultural habit to not like unfamiliar foods. You may be observing this behavior in people with low-paying or no jobs because this cultural habit tends to accompany other cultural habits that tend to limit people to the bottom rungs of any career.
The thing is, poverty is just as inherited as affluence: the children of poor people tend to remain poor all their days, while the children of the rich tend to stay rich. Lots of people change their socioeconomic status, but the overwhelming majority of people do not. And since people tend to stay in one socioeconomic bracket for generations and generations, socioeconomic status becomes a subculture, with its own codes of behavior, its own languages, its own priorities, its own motives.
The affluent, on the other hand, are more willing to try new things because it is seen as sophisticated to do so. To be adventurous with food is really the province of those who can afford to eat anywhere, even if the food in question is not expensive. But one is more likely to find the eat-anything mentality in people who are not poor or rich, but who are socioeconomically mobile.
There are plenty of old-money types wandering around who won't try anything unless their mothers' cooks knew how to make it; go to any country-club in America and you'll find a dinner menu identical to the menus of every other country club, and not very different from those same clubs' menus from the twenties or the fifties. But the people who belong to those clubs tend to not know people who do not belong to those clubs... i.e., you or me.
See, there's another psychological element at work: curiosity. People who are curious are naturally more likely to be socioeconomically mobile because they want to know what the world is like beyond the borders of their own lives, and are not blindly loyal to their backgrounds. They are more likely to become educated, and therefore more likely to get higher-paying jobs. And they are more likely to eat things just to find out what they taste like.
And those are probably the people you find yourself among.
