Actually, Psychologists, Social Workers, and Marriage and Family Therapists do have apprenticeships of a sort- it’s called internship and supervised hours. A Psychologist in California needs 4,000 hours of supervised counseling of clients. Under Supervision, they are not allowed to accept direct payment from a client, but only from payments made to the Supervising Psychologist.
And, they have to pass a licensing exam.
Medical Doctors go through an apprenticeship too. Its as an intern until you graduate from medical school, and then Residency.
So, it’s not just trades that have “apprentices.”
(I was a Steamfitter apprentice for a couple summers while in college. Made great money for a 19 and 20 yr old.