See it like this:
ICO x xruns for, let's say, 1 week at 1 token per USD
Anyone who wants to pay that price for the token buys it in the ICO.
Anyone who's willing to pay more than that also buys in the ICO.
Anyone who wishes their funds to go to the developpers buys in the ICO.
Anyone who wants a lower price waits for a dip in the market, from either bounty hunters, bad news, ...
Once all those people have bought their tokens, price goes back up, as people are trying to sell with profits.
At an early stage, there are a lot of weak hands especially those who own a bounty that has no intention to hold and has no idea about the project,
let's take advantage and buy their cheap tokens.