Or it could have something to do with how the Blues have only drafted 2 Canadian players in the first three rounds of the last three drafts. Also, that "long list" of prospects the Blues passed over includes 6 forwards, 6 defensemen, and 2 goalies. Long, in theory, until you realize that the Blues drafted Alexandrov instead of Clarke and Beckman. You can easily say that the Blues should have drafted Beckman, not so much in terms of Clarke. The Blues also picked Ellis instead of Millman and Spence. This is more debatable on who should have been drafted, but Ellis hasn't done anything to warrant regret at this point in time. He would most likely be invited had he not been older.
As for the rest the Blues passed over, they all came in the 2020 draft. The passed on Cormier, Sebrango, Hunt, Bourque, Grieg, Gonclaves, Schwindt, O'Rourke, Garand, and Levi. These are players the Blues had an opportunity to draft. However, only Garand and Levi were selected after the Blues 3rd round picks. Out of the remaining 8, I think the Blues were more than justified in not taking any of Hunt, Sebrango, Gonclaves, or Schwindt with the 26th overall pick considering no pundit had them in the 1st round. That leaves O'Rourke, Bourque, Grieg, and Cormier as potential 1st round picks that the Blues passed over (and Cormier wasn't selected until the 3rd round mind you). As for the two goalies, I can't say much on them because drafting goalies is a shot in the dark with a blindfold on.
So as for this "long list" of passed over prospects, I think there might be convincing arguments for about 5 - 7 skaters the Blues could have drafted instead of who they got. Even then, that list includes two defensemen that could have selected over Colten Ellis, so you would have to justify that argument by pointing out the lack of value Ellis has in comparison to Millman and Spence. I know that still leaves the two goalies the Blues could have picked, but it should say something that the Junior team invited more 2021 eligible goalies than drafted goalies.
I'm not denying that the Blues 2020 draft wasn't underwhelming at this point in time, nor am I saying that the Blues drafting is close to perfect. What I am saying is that what you posted this isn't great evidence to support your point.