There's another advantage that's probably not very obvious to people who are into bikes. That is that cycling novices are often confused by front shifters. In fact my wife would never shift the front derailleur until after her 2nd triathlon because she didn't really understand how it works.
Can't blame her, the left and right shifter typically work the opposite way from each other. The same button on the left that makes pedaling "easier", makes it harder on the right. Aside from that, a front derailleur that goes out of adjustment can easily lead to dropped or jammed chains.
So in my mind if more gears on the back allows for just a single ring on the front, that's progress for casual bikers.