I was Literature Servant when the "donation" arrangement was brought in.
The Presiding Overseer asked for a meeting with the Secretary, Service overseer, Accounts and Literature Servants, beforehand.
Where he proceeded to hand out letters from the WT telling us about the new arrangement. The letters were full of how they had decided it would be more beneficial not to make any charges for literature. That after much thought the Governing Body had decided it was what Jehovah wanted, as it would make the disciple-making work move forward. Well You get the picture.
I was given a lift home by the accounts servant. He said he thought the real reason behind it was tax. At that time in Britain it looked like that VAT (Value Added Tax) could be placed on the sale of publications from newspapers to books, which was 17.5% at the time, I think. It has never come about up to now, though pressure from the EU may make it so. Anyway if it had it would have meant that on sales of literature in Britain at that about £6 million a year, they would have to pay £1,050,000 in VAT.
Another consequence of the change, was within the congregation. The way it was demonstrated was that you got the "donation" off the householder, kept it separate, then put in the box "Worldwide Work Fund" at the Kingdom Hall. But it was also said that brother/sisters should when they get there literarture, they should put the cost of it in the box. It didn't take long for brothers to realise this meant a double payment, one from them, then one from the householder. Also as some brothers pointed out what if they got a book from literature, put a £1 in the box for it, but a householder only gave them 50p for the same book. Also if they paid a £1 for a book and the householder gave them £2 wasn't that making a profit and they were supposed to be a non-profit making organsation.
Another thing that happened was that brothers/sisters started ordering items like "deluxe Bibles" which were £6 at the time. Also bound volumes, Insight volumes, etc. The whole attitude was "well its all free, now and I'm having one". A couple of years later the WT must have realised what was happening and started to restrict "deluxe" items. Also over time the older publications were stopped, and everything was pared down to "basics", hardback books are becoming paperbacks. Lots of items became "out of stock".
That was going back 7 years so don't know about how it is today.