Can parents book hotels in the United States on their behalf?

Yes.

Official: In the United States, those under the age of 21 are considered minors, and your parents must help you book a room. Each hotel has different requirements. Most of them are 18. A few are 21. You need to ask clearly about the hotel you booked.

Hotel booking is actually an intermediary service that takes advantage of the information asymmetry and channel differences between customers and hotels to sell hotel rooms. Agents try their best to get the lowest price and resell it to people in need of hotels to earn the difference.