Seinfeld is satire. The self-centred and extremely shallow characters are a long-running commentary on typical American sitcoms and their depiction of Christian family values. They treat romantic partners as entirely disposable, they never learn from their mistakes or demonstrate any form of personal growth whatsoever. They treat sex and taboo topics such as masturbation like a game. Heck, they even demonstrate utter disregard for human life, with several characters dying throughout the series and the main cast not giving a damn.
This is in stark contrast to so many American sitcoms which had a lot of stories around conflict, personal growth, forgiveness, and charity. Many of those shows tried to depict idealized Christian family values intermingled with the jokes. Many episodes would feature a prominent personal life lesson in the denouement.
I believe the creators of Seinfeld (Larry David and Jerry Seinfeld) established a strict rule for the writing staff: "no hugging, no learning." This no-compromises dedication to comedy to the exclusion of all else is what set Seinfeld apart from other shows.
The whole 'being about nothing', the vapidness of their personal relationships, how self centered the main characters are. I think it's a good representation of how quickly modern consumer society careened from it's purpose of proving western liberal capitalism was superior to communist polities and descended into nihilism and pleasure seeking behavior once the Soviet Union fall. They even touch on how fragmented urban society had become and how hopelessly isolated we were becoming in the crowd, even before social media.
