I hypothesize that just as Carpel-Tunnel syndrome is a suffering specific to those who sit at the computer a lot, Scruples is a suffering that can afflict those of melancholic temperament who have plenty of free time.
True, I've read about certain Saints having to suffer Scruples, but they were almost without exception Religious or priests who had plenty of time to be with their own thoughts.
Think about it: Religious and priests LEAVE THE WORLD so that they can have more time to pray and concentrate on spiritual matters.
Working at a job 8 hours a day, or taking care of a family of 8, you won't have a CHANCE to dwell on the validity of that confession you made 2 weeks ago. Your mind is sufficiently occupied with exterior things.
A religious sitting in his choir stall making his morning meditation? Of course he has plenty of chance for this.
A mind having hours on end to turn inward is a very, very dangerous thing. I've known several people who had problems with this, and it was always at the phase of their life when they had WAY too much time to sit on the couch all day and brood about things.
For that matter, the Spiritual Masters speak about this as a warning -- to avoid turning inward too much. One way is to focus on God, the sufferings of Our Lord, etc. and not just ourselves and our actions.
I'm not criticizing the religious life (God forbid!), I'm just stating a fact. Scruples is an occupational hazard for the religious and the unemployed, just as a pulled back muscle is a frequent injury for those who do shipping/warehouse work.