Same here (well..shorter period). Carbs-heavy diet makes me gain weight extremely fast and I can't stop myself from overeating. Sorry, that just won't happen. I'm addicted to carbs, so telling me to control myself and just limit the portions makes as much sense as saying to alcoholic "drink just one glass of whisky every day".
And all those vegan diets are insanely stuffed with carbs. In the worst case scenario I could somehow manage on vegetarian diet, assuming I would still be able to eat fish and eggs, but pure vegan? No way. Not possible without turning my life into pure hell.