Part of it is because of Canadian content laws. I stopped listening to the radio on my way to university in the '90s because every second song was from them. If the US had the band rammed its throat, they would be well known there, too.
I'm always going to stand up and defend our cancon laws. They may not be perfect, but they allowed our music industry to flourish.
Know why there's not many well-known Canadian bands from the '50 or '60s? Because Canadian radio station programmers would only play acts that charted in the US or Britain. Outside of Neil Young, Paul Anka, The Band, and The Guess Who, there wasn't all that much. So, there was literally no exposure to be had, outside of word of mouth, unless you were discovered by American A&R.
Cancon laws came into effect in 1971, and even though station programmers still played it safe playing the same bands over and over, musical talent up here exploded in popularity, and we have an
actual music industry that competes on the world stage. (TV? Now that's another story...)