I don't think that boarding back to front is the necessarily an obvious win here. One thing you will see on flights is that people in the back often place their

I don't think that boarding back to front is the necessarily an obvious win here. One thing you will see on flights is that people in the back often place their overhead bags in a compartment near the front. As they do not plan to access this during the flight, it causes them no trouble and saves carrying the bag back and forth. The downside, of course, is that people in the front quickly run out of overhead space while there is still plenty of room in the back. Shuffling bags back and forth is obviously costly and depending upon the prevalence of this behavior may result in less efficient boarding (as compared to front to back).