Something that I know first hand about Mormon tithing is that some decades ago, someone I knew was studying with the Mormons. After a while studying with them, he told me that they kept pressuring him to tithe. He wasn't even part of the group yet. Soon after he told me, I went to his house one day and the Mormons were there and when I came in it was all smiles and handshakes etc. ( of course I was saying to myself: 'Babylonians!') I pretended to be aloof from the discussion they were having with him but I was listening and they were all over him asking him over and over again to tithe.
For JW, FS is voluntary but it is compulsory at the same time because it has to be reported and if a person doesn't participate he is branded as irregular etc. And besides that FS is what being JW is all about.
Getting donations of suggested amounts for wt products and services is all over. The doors are closed for good.
The ball is already rolling. JW will understand that like FS and meetings they will also need to contribute. Donations is something like FS and meeting attendance that they have to do but unlike FS and meetings no one is watching and no consequences for not donating. It is between him and God. JW will understand that donating is part of their worship. And that is how wt will be financed. Up to now, it is like SBF posted, JW figured that by giving their time and volunteering they didn't need to give cash. They will understand that they also need to give cash. That is the bottom line.