When people have good jobs, they realize that they can rely on themselves, and they don't need to Rely on Jehovah™ as the WTS teaches.
When people have good income, they realize that they can be in far better control of the outcome of their lives, they aren't just living at the whim of Time-and-Unforeseen-Occurence™. They can actually plan for their future, have a pension fund, and a home that they own. They don't have to pray and hope and wish for Jehovah's Blessings™, because they can provide for their own "blessings".
When you have people who believe that Keeping Your Eye Simple™ by maintaining a meagre existence in the present will result in a huge payoff in the indefinite future, you have a volunteer workforce that is willing to do whatever is asked of them in order to benefit from the potential payoff in The New System™.
It isn't about money, minimus, it's about maintaining control over people.