Big Mongo prints are the natural outcome of folks building big houses. It has been a factor in portraiture for a long time, and the decision 30 years ago for the 'pro photofinishing' market to encourage photos to be sold as decor. It has become just-how-business is done for a portrait in 8x10 to be sold for a fraction of what it is worth, and a 30x40 to be sold for many, many times what it is worth. If you are sitting on a large room, and want to look up and see your kids' picture on the wall 20 feet away, a tasty 8x10 doesn't turn the trick. A 40" print is fine, and it makes a snappy looking room. The commercial pressure to sell images is real, and not to be ridiculed. We all should be able to work and eat, and if you think being a professional photographer is a bad thing, we can talk about the social value of writing software at another opportunity.
"The Market", the average, affluent person who could write off art purchases (remember those days ?) wants to cover the wall. Thank goodness for guys like Carnie who can MAKE lovely prints that are also friggin' huge, for those of use whose darkrooms are in basements, not former bowling alleys.
(me, I like to look at small prints at arms' length)