I went back and checked and the last year where both Montreal and Ottawa had winning records in the same season was 1978. The 11-5 East Division champion Ottawa Rough Riders would go on to lose in the Eastern Final to the 8-7-1 Montreal Alouettes. Since then, there has been a whole lotta losing.
The above pretty much sums up why the rivalry is not particularly intense. The fact that both cities went without their CFL teams for several seasons didn't help.
I think one unintended consequence of adding a wildcard playoff spot has been that it's cooled down the sense of rivalry among East teams.
Having said that, I think the league can do more to foster and promote these rivalries.
Toronto and Montreal should also be bitter rivals but that just hasn't been there for the past several decades anyway.