Because Canada is committed to keeping the world safe for small kittens and granny ladies. They haven't sold a weapon privately since the 60s and the FAL is one of those evil baby-killer prohibs. There are some governments that still use them, but politics comes into play there, too.
Somebody made the call and assessed that that generation of weapons, which included the Sterling SMG and, for all I know, the last of the 1919s were not worth the expense to store, especially as the likelihood of a fourth-level mobilization had died with the end of the cold war.
You must admit however that they make a darned good razor blade.