There is no such thing as a Universal Theme of Vocational Trust, but there is something at play here, which you might call The Twilight of (Some) Elites. To over-generalize: Un-elected positions of authority dominate the top of the list, especially in medicine. Elected officials and salespeople dominate the second half.
There are a couple ways to read this. First, we trust people we have no choice but to trust. Nurses and doctors and engineers and professors and priests and psychologists aren't merely professionals, they're experts in fields where expertise comes at a high price. Most of those jobs require significant post-secondary education in something the average person doesn't know much about. We trust their honesty partly because we're rarely in a position to prove them wrong.
Source: The Atlantic. Read full article. (link)