Why such huge families?

Call me cynical or even ignorant but i just dont get it! Why do people have 5,6,7,8,9 kids i even saw someone on here the other day who had 12 kids...! Surely you cant devote enough love and one on one attention to that many kids and how the hell do you afford it? Do you have 12 bedroomed houses... I just am baffled by it!