Because they are short on nurses.
I worked with a guy (2012)...he was married to a nurse, and she was getting weekly job offers for the traveling nurse routine (she had five different certifications, and had done a lot of time in emergency rooms). They were talking 100,000 a year, 3 months at a time at hospital with a month of break inbetween, full hotel costs, daily per diem, and a rental car.
I’d tell any person at age 18 today, it’s guaranteed work for the rest of your life if you had certifications and were willing to travel.