There's an important qualifier: loser pays reasonable costs of prevailing party, and the judge decides what is reasonable. It's not automatic. This addresses the concerns about a deep-pocketed party spending lavishly and winning, and the loser being forced to pay a massive legal bill.

(I'm not an expert on the subject, but it's been discussed before on HN, and this is my recollection.)

It occurs to me that an interesting variation would be for the loser to pay an amount equal to the lesser of the two parties' legal bills. That would limit the risk, and remove the incentive for the deeper-pocketed party to spend money just to inflate the bill.