Personally I have been vegan for a year and a half and its mainly due to the fact that I recognise the wrongness in exploiting sentient beings by killing them so that we can eat them, etc etc. Also the DNA of an animal is so close to a human that it could also be considered a form of cannibalism if you eat them (think about that the next time you eat a mouth full of animal flesh)
Certainly animal welfare. After a few years, the thought of something dead in my hands or mouth just seems gross. But, I am also into longevity and a huge percentage of others who are eat a plant-based diet - or. less often, a pescetarian diet- because it is healthier scientifically (not based on some fad diet). It also makes me feel good that I don’t have to worry about nasty odors from rotten meat juices lingering on containers in the trash can (and then my pets trying to tear that apart to get at it). The cost of faux meats pisses me off (it is more expensive than animal products), so I eat either beans or soy shakes for protein. That is a real downside. I love the taste and texture of the faux meats, but cost and availability drive me nuts. I live in an Asian area, too, so know where to find it.