cost, culture, & convenience are the ones I usually refer. gas station hot dogs are cheap and convenient. turning down family recipes put a social strain related to culture. those are two great examples that cover all three. I'm sure you can imagine more: stopping for a fast food burger on your way to protest at the Capitol, etc.
but i have an extremely rare disease that forces me to eat dead animals, animals do it too, plants feel pain, a vegan was rude to me 10 years ago, and its not like me paying for farmers to kill animals and thus creating a demand for meat means i have a hand in it!!!!!!!!