Some of that makes sense.
How is it that in the 60s 70s 80s Canadia teams had no issues winning. Did a switch get flipped in 93?
There are likely several plausible explanations.
1. Quality of information - The first NHL draft wasn't held until 1963; where 16 year old players were drafted. In those days, local scouting was huge, and you couldn't exactly see prospects on YouTube. Given the high number of players that come from Canada, the Canadian teams likely had a bit of a leg up with respect to drafting and insight.
Montreal especially, had a very strong foothold amongst players from Quebec.
2. The 90s saw a long, lengthy drop in the value of the Canadian Dollar. In late 1991, the dollar peaked around 89 cents US. By 2000 it was 67 cents. That made all but Toronto and Montreal small market teams.
3. The game in the United States expanded rapidly in the 90s. Gretzky to LA helped massively. San Jose 1991, Tampa Bay 1992, Florida & Anaheim 1993, 1993 Minnesota to Dallas, 1996 Winnipeg to Phoenix, Nashville 1998, Atlanta 1999, Columbus & Minnesota 2000.
This, combined with on-ice success of American teams (after a 7 year run of Oilers, Habs, and Flames winning), really helped elevate the popularity of the game in the states, making more of these teams "big market teams".
Today, hockey is big business, you've got a generation of players who are armed with advisors on what's the most economically advantageous place to play. Social media, and even the traditional media, have all grown to the point where now in Canada it's largely suffucating. A lot of guys realizing that they can have nice weather, no pressure, south of the border.