Effective Altruism
The vast majority of people understand altruism as an inherently ethical action. Still, a systemic problem with it is that the overwhelming majority of altruistic acts range from at most somewhat effective to sometimes counterproductive. This is often due to not basing actions on evidence, not dedicating our time and resources to the right cause, or even just focusing on something that won't benefit much from additional help.
In light of this, recent years have seen the growth and development of the Effective Altruism movement, which seeks to prioritize causes and look at what the best available evidence says to have the maximum possible impact. Various organizations such as GiveWell, The Life You Can Save, Giving What We Can, among others, have sprouted that help people know how to not only live more altruistically, but able to make the biggest impact they possibly can.
Since Veganism is easily the biggest thing the average person can do to reduce their harm to the world, both to animals and the environment, effective altruists often advocate for reduction in consumption of animal products as part of their ethos, and of course, Vegans who focus on animal rights, should also care about whether or not their actions are having the biggest effect towards achieving their goals.