The scale of suffering inflicted onto non-human animals is so unfathomable that this is without doubt, the most important ethical issue of our time.
One day people will look back in disgust at what we have done to the most vulnerable beings on the planet. The needless exploitation of non-human animals will only end when we take responsibility for our actions.
Being vegan is not a morally virtuous act. It is the moral baseline. Asking someone why they are vegan is comparable to asking someone why they are not racist or sexist.
The question is not 'Why do you choose to avoid exploiting animals?'. Rather, the more appropriate question is 'Why would I choose to inflict so much suffering and death when I could just eat plants?'.
Be Vegan. Get active. Someones life depends on it.