It's because we've seen the ceiling of this team (end of last year and a couple games this year) and they don't play anywhere close to it most of the time. It's ugly football week in and week out recently. They have the talent to overcome a mountain of mistakes but sometimes easily winnable games like their 3 losses turn against them.
Allen is missing reads and throws, receivers are constantly dropping passes, the defense can't stop giving up 3rd & longs to middling QBs, and Dorsey is seemingly way out of his depth. And oh yeah, everyone is either out of the lineup with an injury or playing through an injury.
The good news is that they are talented enough to be 10-3 despite all of this and if they can figure it out in time for the playoffs then they could very well still win it all.