I'd say that the sitcom format is too constricting to keep up with modern viewers' tastes and expectations.

In the 90s, it was easy for a network to pump out a sitcom that followed the procedural format because that it was viewers expected and were comfortable with. But now writers have a different bar to meet. There basically needs to be a serialized element to the plot, which makes it harder to fit things in a comfortable 24minute run time.

Only Murders in the Building is a great modern show that probably qualifies as a sitcom. But its main hook is its long mystery arc. Many of the jokes rely on callbacks to what happened 4 episodes earlier.

Poker Face is largely procedural, but it relies on longer run times and isn't focused on comedy, so it doesn't really qualify as a sitcom.

Sitcoms struggle because they just aren't easy to pull off in the modern streaming environment where audiences expect to consume content by binging whole seasons as a time.