Makes plenty of sense from the airline's perspective. It's price segmentation: people who book 2 days out usually really need to get somewhere, whether it's an important business trip or a death in the family, and so they're willing to pay a lot.

It sucks from the customer perspective - in particular, if you have a sudden illness or death in a family member, the last thing on your mind should be how the airline is about to fleece you. International airlines often have bereavement fares for these situations, but US domestic carriers view it as a profit opportunity. It's often a double-whammy because your travel schedule is often unpredictable in these cases and most airline don't allow flight changes without huge penalties.

Interestingly, I've heard that plane tickets often drop significantly in price if you book really close to departure (eg. < 1 day out). Never tried it, and I don't see it in a quick spot check of the Internet, but it makes sense from an economic perspective - the seat is otherwise going to go unfilled, so any money is better than no money.