Czech Your Math
I am lizard king
There were only 15/70 players from before 1942 and 24/70 from 1942-1967!
Prior to World War 2, Hockey was one of two "professional" sports in North America along with baseball, so plenty of athletes who would be interested in other sports were funneled into hockey
How many Americans were playing hockey then?
Admittedly my historical knowledge is lacking, but weren't leagues being created, folding, merging... weren't players taking pay cuts or not being paid at all... wasn't every team and league suing each other? I mean, just how stable of a sport and profession would this be considered by prospective players and their families. "Gimme those skates and get back to your homework, Jimmy"... "Oh darling, how can we have kids when you might get shipped to BFE and have to take a 50% pay cut without any notice?"..."Hmmm, my uncle's team is getting sued by my friend's team... not sure how that'll turn out or who I should play for... screw it, I'm going to make buggy wheels." My point is that sports in general and hockey in particular may not have been considered as viable professions as they would be in later years. If you don't even know if the league will be around, or if your local team will be, or if the pay will even remain steady, let alone increase, doesn't that affect how many people would seriously train and specialize for a sport like hockey? I mean, kids are in school in the winter, the nights are very short in Canada during the winter, I doubt they were building tons of indoor rinks during the Depression. These are all types of factors which influence the player pool. After WW2, if hockey doesn't work out, you can always find a job, but before WW2, you probably didn't often pass up a guaranteed income to barnstorm for a bunch of back-stabbing bandits. It's difficult to quantify the magnitude of the effect, but common sense says that at least some of these types of factors came into play.
When you additionally consider the smaller overall population in Canada, and the lack of popularity worldwide until much later, it all adds up to a much, much smaller pool of high end players IMO.