It's because 1. NCAA is much, much of a harder league to play in than the CHL. I love watching the CHL but the NCAA is a way higher quality league. 2. Relative to his peers, Hagens was the second highest scorer U19 and the highest draft eligible scorer in the league. And in the WJC U20 (which is notoriously also a 19/20yo league primarily) he was the top draft eligible scorer and the 4th highest scorer on his team, despite playing primarily on the 2nd line and PP unit. He was again the highest draft eligible scorer. And while yes, he had a somewhat disappointing season in BC, you gotta remember that Perreault and Leonard are both 2 years older than him. To be fair he does have a fairly late birthday for the draft but those players are still two drafts apart from him.
I'm really high on Misa too, but Hagens is better defensively, I value NCAA more than CHL, and they're comparable to me offensively, but Hagens had a much better year last year than Misa did. Hagens is one of the top scorers of all time in his D-1 year, in the same breadth as guys like Tkachuk, Hughes, Keller, Matthews, etc. His stats and playstyle are actually eerily similar to Keller's especially.
I've also just watched a ton of OHL/CHL in general (London Knights are my main team) and Misa is really really good, but I've watched tons of guys just like him that have a hard time transitioning to the NHL. It's fun to watch but the league just isn't super good, NCAA is a much harder league, you have to be defensively responsible, scoring is much lower, etc. I really don't know why it's the case either, but for whatever reason Misa has never played in the WJC and I have no idea why.