groovejuice
Without deviation progress is not possible
Nhl is by far the weakest reffed league in north America. Inconsistent calls are the norm and every team is affected by it.
I'm not sure how much you watch other pro sports in NA, but from my viewpoint, NBA, MLB, and NFL are as well, all symptomatic of questionable calls that stick, on an absurdly regular basis.
The following is purely speculation on my part, based on decades of watching pro sports.
I see the reasons as multifold.
1. There is intentional bias, which exists, but is rare. This could be a bias for or against certain teams, players or coaches
2. There is unconscious bias, which is marginally more prevalent. An example would be having heard from colleagues or in the media that a particular team dives alot
3. Incompetence. This can be fueled by ego, lack of experience, or an unwillingness to confer with colleagues
4. League generated policy. If a Ref has been instructed to watch for a particular type of penalty, i.e. diving, he may, by human nature, see an incident that isn't really there. This is especially bad when combined with point #2.
5. Replay. It's absolutely necessary in all sports to overturn a missed or blown call. With modern technology, it's the best way to correct a bad call. Unfortunately, it's hamstrung in all sports by time limitations, and policy. i.e. if a replay instigated to decide whether a puck fully crossed the line illuminates a missed goalie interference, it can't be used.
Also, the plays that can be reviewed are quite limited.
6. The very worst, and one that has been proven in soccer, is gambling. A random ref can always be motivated to intentional make or miss a call by financial encouragement. I'd suggest that this might exist in all pro sports, but that it likely is directly proportional to the amount of money wagered. My guess from most to least would be, soccer, NFL, MLB, NBA, NHL.
There is also the refusal of leagues to address perceived problems in a timely way. We've seen Stanley Cups won and lost with bad calls, perfect games in MLB stolen by horrible calls, good goals in the WC of Soccer disallowed because it's resistance to replay, ridiculously inconsistent interference calls in the NFL.
Obviously, the most common problem in errors by refs is human nature. No one is perfect, and even the very best officials make unintentional mistakes. Yet, whatever the cause, we, as fans, suffer horribly for each and every perceived violation against our team.