I think you've conflated two things.

People can be productive or slackers. And they can be social or antisocial. You personally noticed the social slackers. But I doubt you noticed the antisocial ones, because they're not visibly doing nothing; they're distracting themselves in quieter ways.

I know plenty of people who are both productive and social. Indeed, given that both software and business are mostly team sports, some of the most productive people I know are very social.