I agree that logically it does not make complete sense, but it seems to work. All teams within the course of a season fall into range. I looked at the end of season 5v5 PDO for all teams going back to 2013-14. (Yes, I am that bored at work today.) That accounts for 276 team seasons over 9 years. Only one team has finished with a PDO above 1.025 (2016-17 Caps, who won the Presidents Trophy) and 5 teams have finished below 0.975 (Oilers, Coyotes, and Hurricanes in 2014-15, Avs in 2016-17, and Wings in 2019-20, all in bottom feeding years). So given enough time, a team should find themselves in the middle of the range about 98% of the time.
That's not to say that PDO is perfect. I view it a bit like voodoo because like I said earlier, it works but it doesn't make sense. The point is that if a team is finding itself particularly low or high in PDO, it should expect to trend toward 1 over the course of the season.