Out of college dating
It’s a self-reinforcing story; we don’t accept the idea that someone who looks like Lena Dunham could score with a guy who looks like Patrick Wilson because we never see it in the media.
We never see it in the media because nobody accepts the idea that it could happen and so like an oroborous with an eating disorder, the cycle perpetuates itself.
Whenever we see someone who isn’t conventionally attractive dating somebody who is more attractive we often dismiss the relationship as somehow invalid; clearly he has money, or a high-status job or some other external quality that the more attractive partner desires enough that she is willing to put up with having to toss the cave troll a handy every now and then.
Of course, everyone on the Internet took this in without even blinking, accepting that people are complex and varied in their desires and understanding that attraction is a complicated beast. To judge by the collective outrage over the episode, you would’ve thought that Dunham had murdered Ned Stark while dressed as Hitler and simultaneously shooting kittens out of a cannon that was also on fire.