The Cover-2 got an unnaturally good reputation from the Colts, where a conservative, wait-for-a-mistake defense was perfect. Peyton Manning was (almost) never going to make a mistake, so you just had to wait for the other guy to, and try not to give up touchdowns.
Then with the Bears and the Bucs, you had the talent to take advantage of every single mistake. A missed block was a Warren Sapp sack, a an overthrow was a John Lynch pick. And in Minnesota, the other successful Cover-2 scheme, you have the best defensive line in the league providing enough smother to let the DBs really get some picks.
The Bills chose a defensive system that required an excellent defensive line, landed a bust in John McCargo, and then gave up on the position in the draft. Chris Ellis, CJ Ah You, and Anthony Hargrove amount to the total Jauron investment in the DE position, and they combined for 0 snaps last season.