This of course is overlooking the fact that the league is much bigger now. There were 6 teams in the league for most of the NHL's history. You're talking about going from more than 2 Hall of Famers per team to less than 1 for every two teams.
The 1959-60 Habs won the Stanley Cup and had 8 Hall of Famers. That team used 23 players all year, with 1 of them being a goalie who played 1 game and 3 other guys playing a total of 18 games. Every player on the roster was born in Canada.
Last year's Blues used 35 players, 31 of whom played more than 10 games, from 5 different countries.
The population of Canada in 1960 was 17.9 million people. Today it's 37.6 million people, and the NHL now includes players from much bigger countries like the United States, Germany and Russia, and also gets many players from the Czech Republic, Sweden and Finland.
Also, it's undeniable I think that the level of skill has risen each decade. Even in a much smaller league, there are many players from 1960 who could not play in today's NHL. The league has gotten exponentially bigger and better and tougher to compete in.