I don't know why you keep referencing 2021, several players, including Canadians and players from other countries, were in the NHL. 2021 is a typical WJC year. The only NHL lockout years were 1995, 2005, and 2013. Yes USA did win the 2013 tournament, very strong team. Realistically Canada very likely does win this year if NHL players were loaned, but it would be a carry by Bedard and Celebrini. Some years NHL reinforcements would barely help Canada, or might help other teams more.
The bolded is the key part. Teams aren't just going to forfeit because Canada showed up, the team has to show up and perform. Self inflicted wounds, as in the 2025 team selection, are also a problem. And finally, sometimes other teams play better.
"Other teams have closed the gap" is the same argument people have brought out since the 1970s when they want to appear smarter than they likely are. Some years other countries have loaded teams or Canada has a bad crop of talent, but as you said this was not a WJC where it looked like anyone had a particularly talented team. There are years where Canada brings the best players it has and still loses, but that was not this year... which is pretty much the point of the thread.