Today's idiot people have short attention spans.
The sad state of Comedy
One could just as easily compare the best sitcoms of today with the worst sitcoms of the 70's. But nobody remembers the really bad shows, only the good shows.
But humor is subjective and more about personal taste. If you don't find modern sitcoms funny then don't watch them. Super easy fix. But you or whoever made this video isn't a world renown expert on humor.
And even with Police Squad, it was canceled because audiences weren't, for the most part, catching much of the humor. Even then, the attention span of most people didn't support the format of subtle humor, background gags, clever wordplay, etc. Although, I will say that M★A★S★H, especially in the early seasons, had rapid-fire humor that was easy to miss if you weren't paying close attention — and they weren't canceled. I'd also point out that one of my favorite comedy series is The Andy Griffith Show, and it retained a real-world vibe (rather than surreal situations and nonstop puns), focusing instead on the strength of character development as the basis for its humor. And, as you said, there were a lot of real stinkers on television 50+ years ago. It's easy, I guess, to glorify the past and demonize the present, but I don't think it's fair to do so.