Seinfeld is hilarious.

It was just so popular and unique that everything after it tried to do the same thing and we all got used to seeing this type of humor everywhere. There is a whole TV Tropes page about this called Seinfeld is unfunny.

It's still funny though. If you just pick up a random episode halfway through, you probably won't find each moment-to-moment interaction to be side-splitting. However, if you know the characters, you're just waiting to see which petty societal norm is going to turn into a whole ordeal - like George and Jerry disagreeing about whether moviegoers should pick up their own trash after a movie showing or something. Of course, the hilarious part is when George inevitably loses the perfect relationship with a beautiful woman because her father worked as a movie-theater cleaner and was never home for his family due to inconsiderate movie goers. He leaves his junior mints on the ground, she storms out, and we see Kramer walking into the movie theater with a metal detector as he scours the floor for valuable trash as part of his new side hustle.

It's not a real episode but that's basically the formula and it just works. You are waiting to see how shitty and petty they can be while living up to your expectations of them as characters. You know they never learn a life lesson or gain any true moral clarity. Oh, and my wife especially loves that they frequently do little gags and call backs to previous episodes.

The show itself is just meh, it’s so old it’s not relatable anymore and I didn’t consider it funny in the 90s even. Seinfeld is a perv irl though, he was dating a literal teenager when he was like 40 and nothing really came of it.