I wasn't trying to say that the only reason they do it is for safety. Of course there's obvious building and insurance savings by not having any windows.
As for about having 200 people in a hall...have you ever been to one of em? haha it just feels a little strange...there's one with over 200 people in Seaford, DE. I could only guess because it seems more personal that way...and the less people in each hall, the less the elders have to do. Usually when they have too many people for one hall, they split it up into different sections. We had a French section, and North and South sharing our hall. There might also be structural reasons why as well and things related to that with cost and everything.