Market for vegan burgers that have the same health effect as non-vegan burgers is vegans (including people who try to become vegans). Because if it tastes the same or worse as meat costs about the same (usually more), what is the reason to buy them instead of normal burger or something like falafel.

Market for vegan burgers with better health effect than non-vegan burgers is vegans+health concerned non-vegans which is much larger than vegans alone.

Market for non-vegan burgers is always non-vegans. Being more healthy can affect the standing of particular non-vegan burger among other non-vegan burgers, but is unlikely to attract many vegans (which is an order of magnitude smaller market anyway and couldn't have high impact on the larger non-vegan market).