There are so many ways to eat junk food, even as a veggie, or even a vegan.
While there are health benefits to avoid meat, a lot of people doing it are not particularly health conscious.
It's just that it's a funny stereotype, the seed eating peace lover hippie. Just like the annoying moralist activist or the lunatic product abuser new agist.
But frankly, most veggies I know are just regular folks with regular quirks.