In my experience, the vast majority of people go vegan out of concern for animals, and not primarily because they want to be more healthy.
Doing a quick search seems to support that, but perhaps the trends / reasons are changing as veganism in general becomes more mainstream.
https://vomadlife.com/blogs/news/why-people-go-vegan-2019-gl...
https://vomadlife.com/blogs/news/why-people-go-vegan-2019-gl...