I often hear that athletes are much better now, and that's why every game is such a battle to score goals. I also hear the reason why scoring was so high was that goalies were terrible, and defensemen were pylons in the 80s.
Why were the 50s and 60s so low scoring then? The 70s and 80s were still largely north american talent, so european infusion can't be cited as a reason to increased scoring.
It's just a theory but maybe because there was so few teams they were familiar with each player a lot better making them easier to defend against. This would act in the same way how teams review tapes of games nowadays making players easier to defend against. I wasn't alive back then so who knows. Maybe there someone around here that actually remembers the games, i'm sure they could come up with something better.