[Chos89]

Because feeding meat to 9 billion is unsustainable and the only reason we are able to do it now is because of the huge subsidies. It has terrible environmental effects and it's morally wrong since the only reason people still eat meat is the taste and tradition. I expect a huge paradigm shift here. For more information you could watch documentaries like Cowspiracy and Earthlings.

Edit - Obligatory VSK: http://vegansidekick.tumblr.com/image/151486277095

[inimino]

But people have been saying this (and even making these documentaries) since the 1970s. Has something changed?

[Chos89]

Internet and the flood of information. Vegan population soon reaching a critical mass(every friend circle has a vegan). And then when people have someone next to them who is vegan for x+ years and healthy they will think it's a maintainable lifestyle. Also, anecdotal evidence, just a year ago a vegan post on a forum (i.e. Reddit) would get downvoted into oblivion and posts like 'bacon tho' upvoted, when today, more often than not, it's the opposite