The real explanation would be that this season has been a year of have and have nots, with very, very few teams in the middle.
On the have front, there are actually so many teams with good records that zero teams have locked in playoff spots so far (though Denver and NE are getting close)- as only 7 teams go into the playoffs from each conference, having 8 or 9 playoff contenders in each means the wildcards and even some divisions will be up in the air until the final week.
On the have not front, some playoff contenders have completely fallen off, the unifying factor being Oline injuries (and then QB injuries as a result). Some divisions are so injury ridden (like the NFC South) that everyone is effectively writing off the playoff chances of whomever crawls to the top of the cripple pile by year's end, though wacky things can happen once the playoffs start.