2 of my very close family members are vegetarians. one of them has tons of reasons why including: health, better for the earth (or sm like that), he also feels bad for the animals (he tells my mother not to wear real fur) – even though i don’t agree because if it was causing animals sa’ar then the Torah would prohibit eating meat.
My other family member just went to the farm when she was little and got nauseous when she realized that was the one she ate. she began being a vegan but had to stop because she wasn’t eating enough protein and it wasn’t good for her health. Now she’s a vegetarian.