Perhaps they're souring on him because the gap has been too long. Enough time has passed so that the default response to any criticism can't be "he just took us to a Super Bowl, cram it." Now they have the time to think about why he's considered an all time coach.
If he is/was such a great coach, why did he develop the most sophisticated practice spying system ever seen? Why were only his teams known league-wide for stealing playbooks? Why was his Super Bowl spying tape so egregious it had to be destroyed? Why did only his QB get caught manipulating balls? Why was only his team responsible for having substitutions/formations made illegal the next season? Why would his protégé Josh McDaniels be accused by his own players of doing the same cheating when he got his own head coaching position in Denver? Why can none of his coaching tree win without the cheating nectar and they always come back?
The man was raised on football. He was a ball boy growing up. He has vast football knowledge. But if all that football acumen wasn't enough for him to believe he could win with, then why should it count for you? And if it does, do you go line by line redacting the scandal years and add up the remainder? This goat talk is fit for the politics section of the board at this point.