Injuries and free agent defects and the personnel the team was left with probably would be the best answer. Losing guys like Tate, Miller and Harvin on offense then losing Paul Richardson who was developing nicely hurt, then you add in a O-line the was constantly injured and there would be your biggest issues on offense. Plus you look at a guy like Christine Michael who if he could just get his head on straight could a least be an upgrade returning kicks and mixing it up in the back field for a few plays on offense, but he just can't seem to figure it out I guess. I think he could be a nice weapon, but e must have issues that us fans don't see (or maybe its the fumbles).
On defense losing guys like Big Red, Clem, McDonald, Browner in free agency and having guys injured a lot (Mebane, Lane, Kam, Simon, Wagner, Hill, Louis, Marsh, Williams (Never even got on the field, so who knows), etc The one thing that was a big difference between the 2013 and 2014 team was for the most part the team got most of its best players back at the end of the season, where as this years team was missing quite a few parts or had them playing at a much lower level that the team the previous season and in the end the team was just one play away from back to back titles. Now just picture this team after another good draft, some time to heal and acquiring a couple free agents. Hard to say this team is not one of the top 4 teams again next season, as long as they aren't hit with any major injures in the off season (knock on wood).