It is but a realisation of what was enshrined in the "Hindu Vedas", the Holy Books unwritten in any form till the recent centuries with the printing technology. The Vedas that advocated strongly only vegetarian diet and this was also to raise the mental calibre to higher echelons to love the world and be loved besides exploring and realising the Self or the Supreme, of course in stages!
Only those who were warriors and rulers (besides those undertaking hard physical labour and can burn up or consume demanding a larger calorie intake) were exempt. There was an underlying vision in this ideology. And we see it with awareness of what is happening to the Globe!
Hindus were also advised to reject desire and consumption beyond the basic necessity (eat to 'just live' and but not live only to eat); Also food was treated as 'God given' and any wastage was to be avoided.
Many more Truths, embedded in the Vedas, are yet to spring up with the one on advisability of Vegetarianism and hopefully, they emerge, particularly the 'over developed West / Northern Hemisphere'!
Afterall, it is better late than never!