I've met designers who have publicists/agents ... It helps the designer focus more completely on the design side, what's more important to them... and the agent/publicist can be the one to network for them
It can be too much for a designer to do both
especially when they need as much time as possible to produce a collection to be sold --promotions and networking will just steal all of this time
Also other designers/entrepreneurs I've met I was told they're not really into the 'socializing' aspect and would rather spend time their time in their studio, working...