By making pools appear smaller they encourage independent miners to (continue to) send hash rate there. Thus the evil pool operator doesn't need buy the hash rate himself, he's tricking miners into letting him use it.
True. I suppose creating a fake pool for a long con is equivalent to creating a fake exchange to gather POS coins with which to vote... With the exception that the fake pool will be at capacity for the attack, whereas the exchange voting with stake is much harder to detect, and is passive.