The answer is simple. The larger size doesn't make a difference for most picture quality, seems to introduce some noise at some settings, and results in sensors that take 2-3 seconds to turn on and about 3 seconds between normal shots. What is not to like about increased delay, quality problems and greater expense.
As for cameras like this one, that are at the top of the preferences of many reviewers, the trade off is between the slightly larger (and these are slightly larger), more expensive and the less expensive and smaller cameras that do a job most people find about the same.
Should be interesting to see what next year's technology brings.
