It's competition for mating. Men decide which of us gets the best mating opportunities, because we naturally fall into hierarchies based on - ideally - competence. We follow the one least likely to get us killed and most likely to give us success at whatever-it-is we're doing. Sports, hunting, war, building projects, etc.

We will willingly follow that man, thus raising him up in the mating hierarchy. Women want to be with the man in charge, so, while our own mating prospects suffer as a result, our chances of success at the thing, and reproducing as a consequence of survival, go up, too. Women know this so compete with each other for those men.

So, because women either intrinsically, or are conditioned, to know their value is in their youth and beauty, they compete for those top men. The easiest way to do that is flash bits online as signalling. We men are simple creatures, and are very visual. So it makes sense that women will use what they have to attract the man they want, while having the side-effect of attention and compliments from other men to fill the 'daddy didn't hug me' void.

On the other hand, how do you as a man prove your competence or aptitude for something? By doing it well, or arguing your ideas well enough so you get the chance to lead their implementation. That's where the written media comes in. How well we sell our ideas generally correlates with how well we will convince others to follow them.