You would see similar stuff happen if you look at Most Outstanding Player in the CHL, although not quite as extreme. The elite players generally leave at a younger age. Here is the list. There are some very elite names, but also some ones where you forgot that player even existed. The very best players on that list didn't tend to play in the CHL at 19 (Crosby, McDavid, Tavares, Sakic, Lindros, Lemieux, Lafontaine, Hawerchuk). Now, there are examples of elite players who won it at 19 (Robitaille, Brad Richards, Radulov), guys who are good NHLers (Debrincat, Eberle, and Ryan Ellis) and there are examples of guys who disappointed but won it at 18 and younger (Cody Hodgson, Cory Locke). But, because the truly elite players tend to graduate at younger, there are older guys who stick around and dominate that level. The exact same thing happens with the Hobey Baker, but is even more extreme due to college hockey tending to have even more extreme age gaps, and it being rare for the players who are taken at the very top of the draft to ever show up at college (Since 2005, the only 1st overall pick to show up on campus was Erik Johnson, they have 2 2nd overalls in Eichel and JVR, and 3 3rd overalls in Turris, Toews, and Jack Johnson).
CHL Player of the Year - Wikipedia
