The forward pass was accepted in Canadian football much later than it was in the American game, and even after it was allowed, it took a while for teams to warm up to it. Now, the CFL is known as a passing league, and the run plays much less of a role (read somewhere that 85% of plays are passing plays, not sure if I trust the source, though). Why did Canadian football transition from a mostly running game to a mostly passing game? Do you think the running game will ever return to its former status in Canadian football?
When offenses start to rely more on a running game, Defensive coordinators start to utilize bigger DLinemen and Linebackers. To counter this, Offensive coordinators begin using faster receivers and deeper patterns.
DCs adjust by going to smaller, more mobile linebackers to cover routes, and often to smaller, quicker DEs to put pressure on the QB. OCs then go to larger RBs to take advantage of the smaller defensive players again.
And so on, and so on. Its a game of adjustment and counter-adjustment. The running game will come back.