Why did lots of people only like The Dark Knight because of Heath Ledger?

thats just how people are when celebrities die, notice how a lot of people now are saying that they are a fan of michael jackson, while when he was alive, a lot of people made fun of him, they even laughed when eminem joked about him on his music video, they even called him wacko, but now, they're fans of mj. i personally liked "the dark knight" because it was a great movie, and because of christian bale.