Maybe they're anticipating loss of tax-exempt status.
Extremely unlikely. The IRS has made it clear that they don't want to be in the business of deciding what is an exempt religion. They have been very tolerant of churches that engage in political activity. I think they'd go after those before they tried to revoke the WTBS' status.
As I've said, if they sell off a bunch of kingdom halls and invest the money, they could be set financially forever.
I agree with John Aquila, they're doing something else with the money. I'm going to put my accountant hat back on and see what I can think of.