Some people are vegan because they believe that animals have inherent rights much the same way people do. If one believes that, mass food and leather production is literally atrocious. Aside from the basic idea that you're eating or wearing the animal, the way in which they're kept, transported, and killed can be seen as incredibly cruel.
It's not as far-fetched as some make it out to be. I think most people would find the same treatment for people quite horrific. However, most people have a distinct boundary of Us vs. Them, for people vs. animals. So-called political vegans don't. It's all Us.
The distinction here is from vegans who don't eat meat or meat by-products because they believe it's unhealthy.