I simply don't like the taste of many things. I've never been officially tested, but I suspect I may have extra sensitivity to certain compounds, such that no matter how many other things are in a dish, I can still taste that one thing that I don't like. I also suspect that I am more sensitive to all tastes in general, as there are many foods that have been described to me as "mild" that I find are quite strong.
Now, I'll still try most things once. There are limits, mostly involving spiciness,, but I wouldn't want to be thought of as ungrateful or close-minded. It's just that I've disliked far more things than I've liked when trying new foods.
I also resent the common refrain of, "You just haven't had good [food in question] yet!" Actually, I probably have, and I still didn't like it. It has nothing to do with how it is prepared or what other ingredients are in the dish, that food still has its fundamental taste that I don't like.
It's not food, but I like using wine as an example. It doesn't matter whether it's the cheap boxed stuff from the supermarket or some expensive vintage at a fancy restaurant, because both taste like overripe grapes in addition to whatever other flavours present, and I don't like the taste of overripe grapes.