There is a big difference in paying ten percent of one's income to the Mormon church to how it would be to the JW Org.
The Mormons fund many social schemes which apart from the emotional comfort derived from their nonsensical beliefs, gives the Mormon an important welfare safety net and on top of that, entertainment to boot. In these respects the "whole person" appears to be catered for by the religion.
I believe that in some if not all of the Adventist faiths who tithe, also have social welfare provided along with a healthy lifestyle ethos. Their claims are that tithing is a sacred thing to do for the purpose of funding the spreading of the word.
The JW faith has always played the hard line doomsday cult; believe it or get chucked out. Their financial dealings are usually hidden from the members except their obvious pride and pleasure in property ownership. From soon after its inception it was noted by outside commentators that it invested in property to its great advantage, a habit it has never relinquished.
Surely, if the imminent end of the world was really being preached, it could be organised by volunteers from a small office HQ.
Nevertheless the point is that JWs would be changing their 'spots' were they to justify tithing. Firstly on the religious account that their private sacred beliefs preclude literal application of OT injunctions (unless it is expedient to do otherwise!) and secondly, if they were to justify the vast income generated they might feel compelled to actually give something back!
The fact is that they are constitutionally unable to get involved in any practical, compassionate help for their members, not even when they are the cause of it being needed.