This may be just about vegetarians around me, but often people who are into vegetarianism are also into other forms of food limitations

I think I've noticed this a bit since switching to a vegan(ish) diet 4 months ago. My guess is that once a person starts making diet restrictions, it becomes much easier to make diet restrictions, and once a person starts learning where their food comes from, it becomes easier to find reasons to make diet restrictions (even dumb reasons).