If the pioneers were reimbursed in any way for their field service it may lead to status as employees or agents of WT and expose WT to certain forms of liability. A few years ago there was a case involving a Bethelite and an auto accident where WT was found liable, the settlement was huge. As I recall the determination was that the driver was acting in behalf of WT when he became involved in the accident. Pioneers, regular publishers, brothers with positions of responsibility, are all taught to say that they do volunteer work at their own expense, according to their own schedule, and under local direction. Every bit of that is legal language designed to keep WT free of any legal entanglement.
What some pioneers do with the contribution money they collect is another story.