I think you're overestimating the number of people who are vegan for health reasons. People who are health conscious don't choose burgers - whether they're vegan or not, and most vegans who choose burgers are looking for taste, not nutrition.

It's a false equivalence. Burgers are not healthy - and very, very few people are looking for 'healthy burgers'. People are looking for 'tasty burgers', which is why so much effort is put into replicating the flavour and texture of meat.