Convincing members to quit good jobs that conflicted with the meeting schedules creates a version of the sunk-cost fallacy. Having given up something of value, it will be much more difficult to leave the JWs if they happen to have doubts or issues with the organization. The fear of having given up something and end up with nothing can cause us to mentally imprison ourselves.
It's no accident that the weekly/monthly schedule of a JW is kept busy with meetings or field work. Plenty of time to keep an eye on people, and plenty of ways to make sure they are conforming.