Based on the years my husband and other family were accounts servants, a small minority donated more than $50 every month. It was a struggle to pay the utilities, the mortgage if there was one, and later into the repair/keep up account. Without open accounting like tithing, many jws will never donate...they have nothing to lose. Property does not generate monthly income unless it is rental property. The WTS needs a monthly cash flow like they did back in the when the rank and file paid full price for publications and the WTS investments were viable.
I will say this many non-profit corporations have means for individuals to invest with them and pay less tax on it. But who has money to invest....every jw is told to cut back and struggle on a pittance.