When it became too expensive for an average family to afford
this is a major reason, if not THE major reason.
Hockey has become essentially an elitist sport and has also become a big legacy sport due to overall costs as well. Former players are the ones that can afford all the extra training/personal trainers, nutritionists, summer leagues/tournaments, travel teams, hockey academies, etc for their 12,13,14-year-old kids, which the average middle-class family can absolutely not afford.