famine
it's mostly more expensive to be vegan
i like the taste
you can't get that amount of protein easily without supplements so staying healthy while working out is just harder
your jaw/ teeth can be badly shaped/deformed if you don't eat it while you're growing as meat is some of the hardest to chew food we can readily get. let alone other defects you can get while growing up
if we were in the wild and a hungry animal saw us he wouldn't think 2 seconds before eating us, sure we're smarter and have self awareness but both parties are going to die anyway and want eachother to die for the most part, either for resources or for less danger
also my subjective opinion but i feel like if most people switched to being vegan we'd have a global skinny crisis as most people wouldn't be educated well enough on how to sustain their current weight from just vegetables and fruit