Assembly halls are such a bad deal for local congregations that have to use them. The WTS charges the circuit several dollars per publisher per day (can't remember the exact figure), but back in the 80's, it was something like 3-4 bucks per pub.
The circuit I was in had something like 700 publishers, so for a 2 day assembly, that's close to $6000 rent, which goes right back into the coffers of the WTS!
By comparison, I later moved to a circuit that had to rent a facility for its assemblies. The same two days cost about $3000, and it was really just as nice as the ASSembly hall.
The WTS would much rather get a free $10 million building built courtesy of the average window-washing members, then charge said members $6000 a weekend to use the same building they supposedly already paid for.
What a racket!