A friend used to work ER, any time the computers went down, the backlog in the waiting room would get cleared up. Paper works so much better when you're just trying to save someone's life, and don't know which of the hundreds of different forms you'll eventually have to fill out in the computer.
Because paper record absolutely sucks to retrieve/interpret later, and billing/coding would be even more arduous from paper than it already is with EMRs.