If Mahayana Buddhism is against eating meat, why do some of the Tibetan practitioners eat meat? It is not because the scriptures gave them permission to do so, but for other reasons. As you all know, most of the Tibetan Plateau is unsuitable for growing vegetables and rice. In the area where it is possible to grow crops, the yield is very low. And lacking sufficient transport facilities makes it difficult to have contact with the outside world. Especially in the pastoral areas, there is only tsampa (roasted ground barley) if people do not eat meat.
[Excerpt from Luminous Wisdom Book Series 1: The Right View ~Why Vegetarian?]