The WJC wasn't even that big of a deal until the lockout when no one had any hocky to show and the tournament was loaded with talent and Canadian broadcasting went all in on it.
Like I'm not saying it was a no name tournament type thing but the whole thing of it being this huge event is a relatively recent-ish thing.
Then again I guess that's 15 years ago and kids who were born then and grew up watching it be a big thing are now about to play in it...
Ultimately I would think that as a juniors player, as a kid the WJC is like the pinnacle, the big thing, the "go represent your country at the best tournament in the world (for players your age)". Of course that's big, and for some of the younger guys or guys who don't have that big of hopes of making the NHL or playing pro, it may be more important at that point in time to them than some nebulous concept of playing in the NHL.
A player like Lafreniere has played in multiple WJCs, won gold, won MVP, drafted in the NHL first overall and is preparing for his first NHL season. At this point he's transitioned from a junior to a pro pretty much. The WJC is a cherished memory and high point/milestone in his career to that point. Now it's a whole different game, a whole different level of accomplishment and newer heights to achieve.
At least, that's my thoughts