Humans have more or less empathy for other animals. Some humans (me included) feel enough empathy for other animals, that they choose not to eat them, in order to reduce their suffering. I assume empathy is important evolutionarily to humans to ensure the society survives.

As to "why have empathy for non-human animals?": I don't know, but I guess having a somewhat-arbitrary rule of which animals it's ok to eat, and which not, can lead to a certain amount of congnitive dissonance.

There are also health issues with meat, that don't exist (or don't exist to the same extent) with a vegetarian diet.

Avoiding guilt (if one feels it for being non-vegetarian) feels like it should count towards biological incentive; assuming the guilt felt is significant enough to cause stress, etc.

That's a pretty weak incentive. Even among people who actually choose to experience it, it's far too recent to have exerted any meaningful selection pressure on a species with generation intervals measured in decades - especially given the correlations between the kind of guilty vegetarianism you describe and Western affluence, and between Western affluence and reduced reproductive rate.

I'm talking about personal impact on a single human being's biological well-being. GP framed their question as being for "a homo sapien".

>What is the biologic incentive for a homo sapien to give up 100% of all animal based foods...

That's just it it isn't a biological incentive, it's a moral one.