I'm sure that plays a role for the low match rate, but it's also not something new. People applying for super competitive specialties have historically applied anesthesia and rads as backup.
Like other specialties, the desirability comes in waves. Simple supply and demand. There were 2493 applicants in 2017 and 3287 in 2021 for around the same number of spots. Highly unlikely the extra 800 came from dual applicants.
The reason I am making this distinction is for upcoming applicants to be objective about their chances for matching anesthesia. You know some are going to tell themselves there will definitely be a spot available because the superstars are all going to match derm, ophto, IR, neurosurg, ortho, etc...