"Self-promotion is an essential tool for career advancement [and] networking" (The Harvard Gazette).
In other words, visibility begets visibility because people (rightly or wrongly) believe that those who've been featured in/on respected media platforms are more credible; have greater expertise and authority. Here's the catch, though:
Women are less likely to reap these benefits because, according to research, women feel less at ease with promoting themselves than men- which in turn means that they're less likely to do it. What this really translates to is less access to:
PR opportunities
Clients who will trust and want to work with you
Brands and influencers wanting to collaborate with you
Moral of the story?