Booking a hotel without a credit card requires a deposit. I've had to pay up to a $500 deposit on a hotel stay before. Yeah you get the money back after, but not everyone has that type of money laying around.
Not to mention that the deposit will not be available until 3 to 5 business days after you check out. It usually takes that long for the release to go through. (because obviously in this day and age, technology is not yet fast enough to process a transaction in mere seconds).