There are several reasons many people might wish to reduce their reliance on animal products or become totally vegan.
The first reason is ethical. Many people believe that killing other living beings when there is no need to do so is ethically wrong. Also, as many vegans point out, factory farming is inhumane, with the animals living in constant pain and distress until they are slaughtered.
Next, there are strong environmental reasons for going vegan. It takes several times more grain and water to feed animals to produce a pound of meat than it does just to produce grains for human consumption. Also, cattle, especially. produce methane, which is a greenhouse gas.
Additionally, going vegan saves money. It is far less expensive to buy a pound of legumes (which are high in protein and vitamins) than a pound of meat.
Finally, a vegan diet has several health benefits, including improved cardiovascular health, weight loss, and reduction in the probability of getting certain types of cancers.