I don’t believe that perceived legal liabilities were a factor. I believe that the book study arrangement within private homes provides a much more informal and relaxed atmosphere where friends are much more apt to discuss doctrinal issues.
We were always taught that the home book studies were the most important meeting since they would be integral to the friends keeping in close contact when persecution was launched against the Jehovah’s Witnesses. What are they planning on doing when the Kingdom Halls are bolted shut by the military? Will they meet at Dunkin Donuts? At the local bowling alley?
I think it is clear that they do not want any unauthorized material or discussions underway anywhere. If all of the meetings can be confined to Kingdom Halls, the material and its consideration can be tightly managed from Brooklyn. This was not the case in private homes.
Remember: the Watchtower is paranoid about its members having any kind of doctrinal discussions among themselves. This is why they are reigning in on the flock and clamping down on any displays of independent thought. As far as the gas prices explanation is concerned? That was about as believable as C.T. Russell’s miracle wheat.