Why have the number of power play opportunities steadily decreased since the 2005-2006 NHL season?

Question

According to NHL stats found here, the number of total power play opportunities went from:

• 14,390 during the 2005-2006 season to
• 10,227 during the 2008-2009 season to
• 8,055 during the 2013-2014 season.

In 2005-2006, the lowest number of power play opportunities by a team belonged to the Florida Panthers with 411₍₁₎, and in 2008-2009, the highest number of power play opportunities by a team belonged to the Montreal Canadiens and the Carolina Hurricanes with 374 each₍₂₎.

In 2008-2009, the lowest number of power play opportunities by a team belonged to the New Jersey Devils with 307₍₂₎, and in 2013-2014, the highest number of power play opportunities by a team belonged to the Philadelphia Flyers with 294₍₃₎.

Why have the number of power play opportunities steadily decreased since the 2005-2006 NHL season? Excluding the lockout-shortened 2012-2013 season, there has not been one increase in the number of power play opportunities. Have there been changes, such as rule, officiating, or playing style changes, that objectively explain this phenomenon? Or are other factors in play?

Answer 1

I don't see anything official - there have if anything been rule changes/enforcement changes to encourage calling certain penalties, such as at the beginning of 2013, but certainly there haven't been any official rules making it harder to call penalties (or removing a significant penalty from the books).

My feeling is it's three things. First, as players get stronger/better, it becomes easier to score on power plays - so players are avoiding committing penalties more than they used to. Second, as the league cracks down on dangerous play, some players are avoiding committing acts that might cause a penalty because they also want to avoid suspensions; they also decreased the value of the enforcer (by suspending many of them).

Finally, referees seem to simply be not calling penalties they once used to, and the NHL is largely okay with that. 5 on 5 hockey is actually more interesting - more open - than power plays; while it leads to fewer scores, power plays are often fairly boring to watch, with teams playing sets that are largely not involving big hits or action (until they shoot, anyway). The most interesting thing to happen during a penalty is often a shorthanded breakaway. 5 on 5 is more interesting to watch, so having more 5 on 5 is fine for the folks upstairs - and 5 on 5 scoring is doing just fine.

This article from The Hockey News gives some background, and shows 5 on 5 scoring is still up. This article from Big D, a Dallas Stars blog goes into some of the possible reasons, and shows some more stats.

The one thing that does seem consistent in what I read: the decrease is fewer obstruction or interference calls.