They have really a lot of assistants! For comparison, this term I'll be a LA at the largest Swiss university in a class of ~140 students, we are 1 prof 2 TAs and 4 LAs and we give twice as much homework. Having taken that class myself, I really don't see why we would need more LAs. Unless you want to go the one-on-one hand holding route, also it's not a funding issue, since LAs are basically free. This is probably more due to a difference between the US and European teaching philosophy.