It had much more to do with the fact that Larry Coker wasn't very good at recruiting and developing talent the way that Butch Davis was.
Davis had really built up a loaded roster full of future NFL draft picks, and especially towards his last few years despite having inherited a messed up situation loaded with sanctions. He actually cleaned up the program that had the foul stench of Howard Schnellenbarger, Jimmy Johnson, and Dennis Erickson, and really elevated it to top tier status.
It was easy to see that Coker thrived with those rosters for the first three years. All he had to do was not screw up, since he was handed the keys to a customized Porsche. Unfortunately, he didn't know how to properly maintain that well-oiled machine when maintenance was due.
By the time they joined the ACC, most all of Butch Davis' players (who were primarily developed under Davis) were gone (two 9-3 seasons during the first two years), and they were all gone when Coker had the 7-6 season that got him fired.
In all fairness, that 2005 team that went 7-6 wasn't quite as bad as the record showed, since 5 of those 6 losses were very close, and they did get screwed on a few referee calls that could have swung at least two of those losses.