I truly don't know how many successful candidates are coming through and then eventually accepting the job, however...
During my medical about a month ago, the nurse taking my (increasing) measurements etc. told me he had not done a candidate initial medical for about 3 weeks now....and over the past few months the amount of candidate (pre-initial) medicals he had done has dropped dramatically.
Read into that what you will........
I also flew with a brand new FO from the turboprops recently.
He was a good operator (good situational awareness), and he mentioned that him and a lot of his turboprop mates are planning on staying here just for a couple years to get some big jet time, then move on elsewhere......
Read into that what you will.....
Eternity.