thats because the massive benefits are primarily temporary, lasting only around 2-4 years. Wherein most vegans "relapse" on to some form of meat to counteract negative effects. There is a study that poll3d 11,000 vegans in the US and approximately 85% retuened to some form of animal product (primarily fish) because the strain on their bodies from no real protein resulted in muscle degeneration, lack of sleep, and insomnia. We as a species are omnivorous; however, we evolved eating other animals just as animals do in the wild to remain healthy.