Retired accountant here. I thought I was done explaining the Henrietta O'Reilly trust but I guess not.
The US tax code, enforced by the IRS has a lot of rules regarding trusts. First of all the beneficiary (in this case the Watchtower) has no say in how the trust is managed, subject to what is written in the trust document. Additionally if the beneficiary does not want to accept the trust, he has a limited time to do so, after that they're stuck with it.
My guess is that O'Reilly set up the trust which started sending money to the Watchtower, which didn't pay much attention to where it came from. Now they can't divest the trust.
I'm on the road, my ability to get on this board may be limited. If somebody wants more information on trusts I'll dig it out for you when I get home.