the lifestyle vegetarianism actually started around 600 BCE within the two religions of Buddhism and Jainism, not the 21st century aka the 2010s in California in America as some "liberal propaganda".
it was supposed to keep us healthy as in a permanent cleanse (both physical, and mentally), and it was the basis of the straight-edge lifestyle as well that obviously came waayyy afterwards in time. meat, alcohol, and any other related ordeals were proven to do us and the planet more harm, so these religions desired change and encouraged
the idea of living longer by treating the planet and our bodies as these protected temples. it was never forced though, and it was a choice. however society/religion turned it into a force/mandated thing through time like every single religion does.
in the current timeline, vegetarianism is still common within the countries of India and Thailand - but Thailand is more complicated with it by the society following the religion but not following it, while India is more strict with it still.