For the last 20 years or so that I was a JW I also don't really remember anyone who could be regarded as "stable" actually proceeding to baptism other than relatives of JWs. The (very) few that came along always seemed to have some kind of issues.
One thing I did notice was that quite often the studies people had were also being called on by the Mormons and / or other Christian groups that did outreach programs. The impression I got was that this was the same small pool of people who tended to be very needy , often with very few friends and somewhat social pariahs who were delighted when someone would take an interest in them. Often when the study got to the point that they needed to show some commitment ( such as going to the meetings regularly ) the study was stopped , either by the publisher or by the individual.
When I was pioneering , I had a study for about five years with a widowed older guy - it developed from a long term magazine route. We used to have interesting chats - the guy had a fascinating background with the British army and had been badly injured and invalided in the Suez campaign of 1956.He didn't have any friends and his family very rarely saw him as they lived far away and weren't really interested in him.
I would bring him to the Memorial and an occasional special talk etc but otherwise he wouldn't go to the meetings. I was kind of aware that he would never become a JW but it was more of a social call and easy time for me , especially during the winter. It also gave me a bit of kudos in the congregation and I dined out on the fact that I had a study for much of this time! I think a lot of bible studies are on this basis , especially for pioneers desperate to get their time in. When I stopped pioneering I just downgraded it to a monthly Sunday visit with the magazines and eventually he was hospitalised and the call fizzled out. I still miss our chats though.