Why did Toronto get stuck with the YYZ airport code?

Have you ever wondered why Toronto ended up with such an unmemorable airport code as YYZ? Probably not, but I have. Miami has MIA, Berlin has BER, Vienna has VIE, London Heathrow has LHR, and Toronto has ... YYZ. What gives?
Well, if you look it up, the explanation goes that the International Air Transport Association (IATA), which is responsible for such things, decided, in its infinite wisdom, that all Canadian airports should have a code beginning with Y. Thus, Vancouver is YVR, Winnipeg YWG, etc. I have never seen a good explanation for exactly why this first letter requirement applies to Canada, and not to the USA, Spain, Japan, etc. I understand that there are many more countries than the 26 letters of the alphabet, but why Canada should have this stipulation and not other countries, I have no idea.
So, given the initial Y, I can see why YVR works for Vancouver, and YOW for Ottawa. But YYZ? Well, the explanation given is that YZ was the old telegraph identifier for Malton, Ontario, which was the nearest town to where Toronto airport now sits. An explanation perhaps, but not a very convincing one. YTO does exist, but it is the umbrella identifier for all airports in the Toronto area, including Toronto (YYZ), Billy Bishop City Airport (YTZ), Hamilton (YHM), and Waterloo (YKF).
And, in case you were wondering, TOR also exists, and it is the code for Torrington Municipal Airport, which is just outside Torrington, Goshen County, Wyoming! Seems kind of unfair, don't you think?