For any continuous source of entertainment, there’s a point where the creative energies simply seem to wane, and the entertainment turns into “entertainment”.
The term for this is “jumping the shark”, from an episode of Happy Days where Fonzie jumped over a shark in water skis. I never watched the show, but get the feeling that episode must have seemed bizarre.
The Matrix reached this point about 10 minutes into the second movie.
I’m not quite sure exactly when Dilbert stopped being reliable. I usually only check it about every two weeks now.
Other comic strips have failed to be funny for years. Notable is Garfield, which ran out of juice about 15 years ago.
Tofik Benedictus Hinn is probably more or less immune to jumping the shark.
For this website, that point was June 4.