It takes time for player safety to catch up, whether on a cultural or other level, as Jacques Plante did when he introduced the NHL's first goaltender mask. After this cultural shift, players had to wear helmets starting on June 1, 1979, unless they were professionals prior to that time and were able to opt out with a waiver.
The greatest hurdle to change may be the difference in viewpoints between the older and younger players in the league, since younger players would prefer the new equipment. On the other hand, veterans:
After Chris Montador passed away in 2015 from an overdose but the NHL ignored the evidence of his traumatic brain damage as a consequence, one can't help but believe the NHL is beginning to pay attention to the negative publicity and the fallout from the Chris Montador incident.