New Constitutions are usually written just before or just after revolutions and are written by the revolutionary forces.
Believe me, Canada does not want to see any sort of violent uprising which might involve armed Americans attempting to take over government and rewrite the rules and I suggest that any attempt to replace the Constitution would be met by every armed American as a threat worth fighting for.
For good or ill, that is the situation as it is and as it shall remain until there is a fundamental change within our society.
Despite the need for that document to be updated ever so slightly there is no chance it will happen within our lifetimes.