Seinfeld wasn't just a popular show; it was a cultural leviathan. I didn't start watching Seinfeld until my late teens, and I used "yada, yada, yada," well before my 13th year. It was the 90s pop culture equivalent of an airborne infection akin to The Simpsons and Jerry Springer. Logically, NBC sought to continue the show's success even after the final episode aired, but making a successor series is a rough gig for anyone.
For a long time, the prevailing wisdom was that sequels and spinoffs sucked. Even if the studio had the best intentions going into a spinoff, capitalizing off the success of a critical and commercial hit is an extremely tough terrain to navigate. If you go in an experimental direction, the general audience might feel that the charm of the original is gone. In opposition, if you try to play it safe and repeat the formula of the first entry, the audience gets bored.
In their attempt to keep the Seinfeld cash cow buoyant, NBC ordered a succession of spinoffs staring the core four of the cast. Essentially every show sired in the vein of Seinfeld did their best Hindenburg impression after a season, but my favorite flop of the bunch is The Michael Richards Show. The YouTube channel Hats Off Entertainment gives a retrospective on the failed series in the video linked above.