Easy, because everyone wants to buy "at the bottom", so the bottom comes and sits there for an entire year while they look at the screen and say, "hmm seems pretty stable here, looks like the bottom is in, but I think i'll wait and see if there's a flash crash, then I'll buy some then".  Then the train starts to leave without them and they realize they're a fucking idiot.

That and shorters are good at keeping the price from moving...until they fail and lose everything: