Some people become vegan solely for the health benefits. And there are many health benefits associated with veganism. But just as the word vegan means different things to different people, what constitutes a health benefit is different to different people. It is no secret that people following a vegan diet have less problems with obesity than people following other diets. Some people are interested in managing their weight because they believe they look best at a certain weight, while some are obsessed with body mass index (BMI). Some people want their skin to be clear. Some want to reduce the probability of heart disease. Many elite athletes are turning to vegan diets specifically because of the performance they want from their bodies. This is happened in endurance fields such as marathon running. It is also happening in body building (https://www.greatveganathletes.com/category/vegan-strongmen/).
Then there is another group of people that see health benefits in terms of longevity and health in old age. All of these benefits can be found through veganism, and are not mutually exclusive.