Because they have no power and we get to hold the actual elected leaders in contempt, as is right and just. The alternative is electing one, and that kind of worship messes with people's heads. Look how bonkers some Americans get about their blessed president.
I don't agree with the argument that having a Monarch somehow shields Canada from worship of it's leaders, or enables us to hold our leaders in contempt. Absolutely no one in country thinks of the Monarch as our head of state except in a technical sense. The Prime Minister is for all practical purposes. Having a monarch in no-way shields Canadian leaders from hero-worship. Nor does it make Canada uniquely able to hold politicians accountable. It's our Westminster-style parliamentary system that (somewhat) achieves that by concentrating less power in the hands of an individual, which could exist independent of the Monarch. It already essentially does since the King-Bing Affair in the 1920s cemented the Monarch's influence as purely ceremonial.
The status quo has a lot of momentum and you need some sort of catalyst to make the change. Liz managed to avoid much controversy so that catalyst never appeared - perhaps her death will trigger the will to change it
