I think it's two things. This is not a tournament Canada takes as seriously as the Hlinka. It makes little sense. It's the official World Championships for the age group. Hlinka is merely the tournament more convenient for CHL teams. I don't know why they couldn't upend the CHL playoffs. The USHL upends their playoffs with a full team missing, and I'm pretty sure there are also players missing playoff games in the top junior leagues in Finland, Russia, and Sweden every year, but I don't think it's changing.
Normally Canada may not send their best, but they at least have the second best roster based on pure talent. I remember some of those Canada teams that weren't even that good with players like Cozens, Smith, Drysdale, Laffy. The reason as you say is the players don't play together as often as the USA and some of the other countries. This year, I don't even know that you guys have the second best team. There are a few big talents like Bedard and Fantilli, but I think Hockey Canada was put in a very difficult position with constructing a team entirely without one of the three leagues, and then even less options from the O and W than usual. Still possible Canada can win this thing, but it's an uphill battle. For once you guys may play the role of underdog.