I understood the basic issue in the Jimmy Swaggart case was whether tax needed to be paid on 'religious' books and magazines that where sold?
And that was an important principle that would effect many religious organizations
The JWs were effectively selling their publications, so if tax needed to be paid, the WT would have needed to also pay the tax - hence the WT had a 'vested' interest in the outcome of the court case.
The WT thus became a:
https://www.google.com/search?q=friend+of+the+court
someone who is not a party to a case and is not solicited by a party, but who assists a court by offering information that bears on the case.
And of course, following the case, the WT went down the 'literature donation' path... which some believe was the first 'trigger' in the WT's apparent financial problems that continues to have ramifications down to day - by removing a consistent revenue stream - maybe they should've just kept charging, and paid the tax...
there's more here, as you may have already read:
https://www.jehovahs-witness.com/topic/129627/jehovahs-witnesses-jimmy-swaggart