Humans have stuck with flesh long after it was strictly necessary in an evolutionary sense.
Sure, it's not a strictly necessity, but have you payed attention to how hard it is to be strictly vegan? Evolution isn't going to pick what's morally right, it's going to pick what works best.
I think you're confusing veganism with vegetarianism. Vegetarians don't eat meat, which is doable. Vegans try not to consume or use any animal products at all, which is near impossible. For example: dairy, honey and chewing gum are out of the question, as well as the use of beeswax, leather and products tested on animals.
Veganism is a recent, Western, movement. Vegetarianism has been around for millennia and is practiced by hundreds of millions around the world. In India alone, 40% of the population is vegetarian.
Not really hard imho. At least as long as you are living in a major European city, but I would assume North America/some other places should be similar. Have you actually tried?
Sure, it's not a strictly necessity, but have you payed attention to how hard it is to be strictly vegan? Evolution isn't going to pick what's morally right, it's going to pick what works best.