What motivation do people with social skills and those norms have to help those with less social skills? >Because unless there's something in it for them they're not doing it. Many of the kind of people who have >social skills find hanging out with the kind of people who don't actively unpleasant.

I would say that if the people with the high social skills have the option of removing the people with low social skills from the group then there is little/no incentive to help them beyond perhaps altruism.

But in many situations these mixed groups are forced, and teaching the people with low social skills to interact according to the understood cultural rules can make them more pleasant company. So if you're continually forced into an environment with someone, improving their social skills can be of direct benefit to you. Examples would include a coworker in a team work environment, a family member or in-law, the roommate or significant other of a valuable friendship, etc.