The US is not a hockey country. Last season, the average SC playoff game was watched by less than 830K Americans. It's very sad.
Unfortunately, there are many barricades that have prevented hockey from truly becoming more mainstream - and I'll spare us the essay outlining those reasons.
But I will call attention to two big issues:
1. The NHL has often shot itself in the foot when it comes to hockey, between lockouts, poor marketing and other decisions. In a span of 20 years, the league had 4 labor stoppages that have wiped out the equivalent of two full seasons. One of those seasons came after the team in the largest media market in North America, ended a championship drought, at a time when hockey was the new "it girl" in pro sports in the states. They've never quite had an opportunity like that ever again, and those opportunities don't come around often.
2. Hockey is a sport that is significantly better live, especially if you're "new" to the sport. It's much easier to get someone interesting in hockey after taking them to a live game, than it is to show them a game on TV. Unfortunately, the cost of attending a hockey game in a lot of places isn't always family friendly (it's also not a cheap and easy sport to pick up and play). You have entire segments of the population who would love hockey, they just don't know it and they're not getting the opportunity to find out.