I would be really interested in hearing a recording of the GB meeting where it was decided. But alas...! None such exist.
I could speculate though.
I know of a case in Amherstburg Ontario where someone fell down the stairs at a book study. Or is that balk study...
Anyway, it was a sh*t storm. Talk about causing division. The homeboy encouraged the visitor to sue him, otherwise, how do you get the insurance to pay out? So, visitor gets a lawyer. Lawyer sees dollar signs. The rest is history.
But there's still a better reason. Resources....
Dubs have a limited amount of loot, and guvernin' buddy-boy wants to get it all. When I was young, there used to be a contribution box at the book study home. And people put in loot. The conductor did the collectin'... Made out a reciept and took the loot. The loot went to the Society.
I remember thinking (when I was young) , hey, that's great! Some money for the poor brother whose house were wrecking with our traffic.
Ahhh to be young and green again. Well, we know where the loot went now don't we?
In any case, the Watchtower Society was not getting any loot from the book study. The practice of collection at the book study kinda fell away. So, the book study was no longer profitable for GBoys. Only a drain on resources. All expenses, no revenue.
I submit that the real reason the book study was ended, after all the years of talking about how damned allMighty important and "vital" it was, is simply that it was not generating revenue.