I have a strict diet as a part of my exercise and training program, so exploring the unknown makes me uncomfortable.
I can't calculate the nutritional content of new foods if it's just at a friends house or at some sort of event, and even restaurants it can be difficult to find out the nutritional content/calorie count or also might not have any of that oh-so-important extra details to me.
I don't just eat when I'm hungry and when I need to.
I eat specific foods, in specific portions at specific times, whether gaining or losing weight, so any sort of disruptions to my schedule are difficult to cope with.
Even when eating unhealthy, which I'll admit I do so more often than I'd like to, I stick with what i know, and this is actually ideal as I've read our stomach's gut bacteria gets use to whatever we eat so new foods, unhealthy or healthy, will taste strange to us.
This means because i've eaten healthy for so long, many unhealthy foods can make me sick, aside from a few unhealthy foods i have often enough that my stomach is still familiar with it.
Don't get me wrong, I'll try a new food occasionally, and when in a situation when having dinner at a friend's house or such, I'll suck it up and give it a try, but I have a very low chance of liking it, probably a 5% chance.
Sometimes I'll force-feed just to be polite, sometimes I just can't do it and try to politely reject ("I already ate, I'm good thanks.")