Well....most of us are traveling on business...Priceline requires pre-payment ...I don't know about others but my trips change quite often...leave early..stay longer....this means you lose your money if you check-out early...and what if you need to stay longer? Your corporate rate may not be available ...have to pay RACK rate or possibly even switch hotels.
Bottom line....Priceline is tough for a lot of us to use due to changes in plans....it's OK for leisure though where one would not change.