I would contend that parents ought to be the ones teaching social skills, and that the history of humanity suggests that parents have been net more effective than third-party professionals.
Of course they should. And do. And yet, I would contend that there are some particular skills that it is hard to teach within the home, by parents alone. Negotiating in a team of peers, for instance (if one does not happen to have half a dozen siblings). Getting attention in appropriate ways when one is in a large meeting.
For some kids, it really does take a village.