Because their business model is your little sister listening at the door, then running to tell everyone your news before anyone else can, so she can have the social capital gain of being first in the know.

You can't be the first to react to price changes unless you can hear about them sooner, process them faster, and issue responses sooner than everyone else. If your business model is "buying just before everyone else buys and drives the price up" and "selling just before everyone else sells and drives the price down", you need to turn yourself into a paperclip maximiser using ever more resources to try to out-compete the other companies doing the same.