Vegans are in it for ethical reasons, not specifically health. They just don’t like the killing of cows, pigs, chickens, etc. as they see all animals the same - why do we not kill and eat dogs and cats? When you can choose a plant burger that tastes the same as a beef one, but no animal had to die for you, they choose the non-cruelty version.
Whole food plant based is a healthy vegan diet.
So - there are healthy eating vegans and junk food vegans! Red meat and processed meat has been proven to be bad for your health. Eating whole food plant based is healthy.
Healthy vegans eat a wide range of fruit and veg, legumes, beans, etc. and avoid processed foods.
Overall though I think the science still points to a balanced vegan diet being healthier than a balanced omnivore diet.