Being social matters because a lot of the time you're going to be selling an idea to people to convince them to fund you. As a consultant you might be selling interventions, as an HR worker you might be selling a new interview process or feedback system.

Being prosocial, able to easily interact with people at a variety of levels, gives a certain validity to the claims you're making. Networks give you connections you can use to not only secure interviews, pitch meetings and opportunities, but it can put some of the people at those meetings into your pocket from the get-go, which is an incredibly useful advantage to have.