1, cats cannot survive on a vegan diet, even if they eat it, they're not being given their needed nutrients
2, a cat isn't capable of understanding the moral grounds behind a vegan diet
At the end of the day, it's be better, not perfect. Don't force a carnivore to be a herbivore
Besides cost, the barrier to trying vegan food with my cats is having a vet on board.
Vets are hostile to the idea of veganism just like most everyone else- plus their profits depend on hocking this or that food, even suggesting trendy anti-scientific diets like raw meat.