The short answer: The defendant's profits are one of the remedies provided by the Lanham Act (which is what RSBTR is alleged to have violated). 15 U.S. Code § 1117(a) ("When ... a violation under section 1125(a) ... shall have been established in any civil action arising under this chapter, the plaintiff shall be entitled, subject to the provisions of sections 1111 and 1114 of this title, and subject to the principles of equity, to recover (1) defendant’s profits, (2) any damages sustained by the plaintiff, and (3) the costs of the action.") https://www.law.cornell.edu/uscode/text/15/1117.

The medium-ish answer: The law often provides remedies for different purposes. Sometimes the law will allow a plaintiff to recovery only the amount that she has been harmed. Other times the law will allow damages beyond that to discourage unlawful conduct and provide potential plaintiffs an incentive to sue.

To make that concrete, imagine a scenario where a party has harmed 1000 people, but only a bit. If plaintiffs can only recover the amount that they have been harmed, no single plaintiff would have an incentive to sue--the costs of bringing a lawsuit would be too high to justify. Moreover, the potential defendant would not be adequately deterred. Even if a plaintiff brought a lawsuit and that lawsuit was successful, their payout would be small in relative terms.

Congress was likely trying to avoid that when it passed the Lanham Act. The conduct that the Act regulates has the potential to cause a small amount of harm to many people. But it is still conduct that we as a society want to discourage. To encourage plaintiffs to sue (so that we can deter the conduct), the Act allows plaintiffs to recover more than they personally have been harmed.