Students of the Work and Travel USA program can work in the United States as a service staff of various establishments, such as:
Pool lifeguard/Ocean lifeguard
Also, seasonality plays an important role.
Americans are not interested in temporary jobs, and since work is relevant only in the summer at resorts, they have a need for participants in the Work and Travel program, and there are much more options for working in such places.
On the website of the US State Department and sponsors, there is a list of works that are prohibited.