They get it, but refuse to accept it. They are in the business of trying to convince as many gullible people as possible to support the Leftist agenda. Polls are merely one weapon in their arsenal to accomplish their goals.
President Trump has been amazingly successful in pulling the Leftist media's mask off. "Fake News" will stick, as will the example he's made of CNN.
Thay get it, but their hatred for all that Trump represents prevents them from thinking rationally.