All TV shows have a shelf life — nothing good can go on forever!
Usually, this decrease in quality is slow. But sometimes, something happens that is so ridiculous or badly done that it pushes a show past the point of no return. This is called "jumping the shark."
Like on Pretty Little Liars, when the girls were arrested for Mona's murder, kidnapped and put in an underground dollhouse, then discovered Mona was actually alive.
I know some people thought bringing Michael back from the dead was too much even for a telenovela like Jane the Virgin.
...Or that having Felicity redirect a nuclear weapon to kill tens of thousands rather than hundreds of thousands (and then it sort of being brushed off) was way too far on Arrow.

