NHL stats are just for the regular season since everyone plays the same number of games during the regular season. If the Oilers miss out on the playoffs one year, it wouldn’t be too fair to McDavid if the other superstars got extra games to improve their season’s stats where he didn’t.

To put it into an example, let’s say you’re comparing the seasons of two players, A and B. Player A makes it to the playoffs, player B doesn’t. Player A scores 46 goals in the regular season and 5 in the playoffs. Player B scores 50 goals in the regular season. If you include the playoffs, it looks like player A was the better goal scorer for that year, but that’s only because he played more games. Getting to the playoffs is a team victory, not just an individual one, so punishing a great player stuck on a bad team by having other players who made it to the playoffs have comparatively better stats isn’t fair.

Playoff stats are still tracked, just separately. So you can still compare with playoff stats if you want to, it’s just not the default.

Lots of answers here, but let me give you an alternate viewpoint, from the NHL.

"Fuck you for caring about the sport, now give us some more fucking money! You want stats, hire a statistician. Except you can't because you're a POOR FUCKER!"

"Now shut up and buy another watery $35 beer."

To allow even comparison across teams that play a different number of games. It's a very different proposition to get 138 points in 82 games vs 110. In soccer, it's common to quote statistics as "per 90 minutes" for just this reason.

Pretty sure all pro sports do this.