Big issue and no doubt many studies exist that provide some answers much better than mine, but here are a few thoughts
First, in the decades up to the 1960s/1970s, church attendance was part of the social scene.  Belief was an element, but it was not a deeply held or deeply felt aspect of attendance and participation.  The decline started in those years as social norms shifted and it started becoming less a part of the social scene, which then accelerated.  The Quebec situation was exacerbated by the malign effect of the Catholic Church that was rejected as part of the Quiet Revolution.  Once the habit was broken, then lack of deeply held belief and outright skepticism of the main tenants of Christianity meant that going back didn't happen and won't.
Second, conservatives in this regard retain  belief and are not looking for anything to reflect on they want certainties that once provided work for them.  Liberals find the fantastic aspects of faith impossible.