If I'm understanding your question correctly, a huge amount of our behaviour towards food is learned. Our instincts are rather limited (and worse than useless in the modern food environment) in determining what we should or should not eat. We're very much dependent on what we experienced growing up. There's a reason children put everything they can find in their mouth (well, several actually). And as a social creature we benefit from the knowledge passed down in the meals of whoever raises us. And this is possibly the most important thing we learn, it gets pretty hard-wired into our brains because it's a fundamental issue of life and death.

So a lot of 'regular' people are restricted by their upbringing. Many, particularly when looking at paleo-type lifestyles, attempt and sometimes succeed at breaking their previous food associations and learning to appreciate different types of food. And that's usually because they understand rationally that these things are nutritious and as a mature, healthy human they ought to be able to eat them. It happens on a lower level for some people with certain vegetables, it happens for former vegetarians and meat, and it happens for 'regular' people with meat and two veg. They accept that it's a cultural distinction that is counter-productive much like an addiction to bread at every meal. And that the paleo thing to do would be to eat every edible part of the animal. But in general the paleo lifestyle isn't really about going out of your way to eat things that aren't readily available for no good reason. You might be able to argue that people need to eat more live and suck the marrow out of bones but it's still a judgement call on the availability of those items where you are and whether it's worth the physical and mental effort of including them in your diet.