There are two types of vegans: the ones that will tell you why you should become vegan too, and the ones that don't want to explain why they are. The second kind just behaves like that to differentiate from their militant peers. Even if you are interested you probably won't get too much information. So here it is.
One of the most striking arguments in favor of a vegan lifestyle is its sustainability. It is highly inefficient to feed chicken with tons of corn that we might eat as well. For this reason animal products require more than ten times the resources (water, energy, arable land) of vegan food. The exact factor depends, of course, on what kind of plant/animal you consider, whether it's organic or not, and so on. So for the future of our planet it is beneficial to restrict from animal products at least once in a while.
Minimalism and eating vegan go hand in hand. Get more out of less. Cherish what you have. Be lean. Smile.