I haven't kept track of the score trend in past years, but people have been saying the sections on the test are much harder this cycle than any of the practice tests available on the site, while in previous years, AAMC 10 and 11 were said to be good indicators of what to expect. So it could simply be that, along with the other changes to come with the MCAT, they've just made it harder, but they haven't updated any of the practices to match the actual difficulty.
I haven't even taken the exam yet, so this is all speculation.