I understood the title more as, "since we all know other people's bragging is insufferable and does little to convince us of the bragger's supposedly higher status, why do we continue to brag ourselves as if we believe it will have the intended effect on others?"

The answer, and the article gets at this in the last section, is a variety of anxious human emotional impulses. I guess we knew that, but the way the article teased it apart was interesting for me anyway.