CFLsteve made some excellent points about the SAM position, which is absolutely unique to Canadian football and without equivalent in CIS, US college, or NFL.
To his post, I'd just add that CFL defenses have evolved schematically to take away the West Coast offense that Trestman and Hufnagel popularized from 2008 onwards. DCs have figured out that pressure and combo coverages behind the defensive front have a statistically better chance of success. Take away the short game, pressure the QB, and dare him to beat you with low-percentage deep balls down the field.
LaPolice has an excellent column on this very issue: http://www2.tsn.ca/cfl/story/?id=461018
The four main reasons LaPo lists are Canadian ratio-changers, addition of a fourth DI, personnel changes/injury, and evolution of defensive coverage. On the latter topic, he notes:
Defences have had to evolve to handle the offences of today and they have done a great job of it. When I was a coordinator in 2002 and 2003, the coverages you would see were much simpler; a lot of man coverage and forms of Three Deep coverage. Now a days, there are a lot of combination coverages and what is called pattern reading where DBs and LBs run underneath and right to cover the routes that they recognize compared to dropping into designated zones on the field. The defensive coaches in the league are very good and know what they are doing. They deserve a lot of credit for the job they do.
The point about combo coverages is important. Instead of just playing straight man or iterations of 3 deep, defenses are employing a mix of man and zone coverage on a given play, made possible because of the football intelligence of DBs who can pattern-read on the fly. The latter type of player is much harder to beat than a DB who just drops into a particular zone or plays straight man. You have to actively scheme to take him out of the play, and if you do, you expose yourself elsewhere.
My overall point is that everything is cyclical. Defenses have responded to offensive changes over the past seven or eight years. Now the onus is on offenses to catch up. We've already seen versions of the new CFL offense with what SSK is doing with a three-pronged ground attack. The Als were actually forced to adopt a similar playbook in 2012 due to injury and this year, they are slowly incorporating just such an attack with Whitaker, Sutton, and Rogers as the end-around threat comboed with the odd QB draw.
OCs will eventually realize that jumbo sets and a multi-dimensional ground attack are the keys to attacking a pressure defense. Once teams adopt that strategy, defenses will be forced to evolve in their turn.