Well, you've currently got Johannes Dale-Skjevdal at the IBU Cup, he was 3rd in the World Cup overall last season, and it's not even the first time he's been demoted either. Johan-Olav Botn was 3rd, 10th, 5th, 7th and 14th across the final two World Cups last season and not only could he not secure a World Cup spot this season, he isn't even first in line for promotion, having been passed over for Uldal and now behind Dale-Skjevdal in the queue. And Isak Frey is knocking on the door too, he hasn't been outside the top 6 in any race this season, finished 5th in the IBU Cup last year after not even doing the first trimester, and won three golds at the Junior Worlds, and he can't get a spot either.
Hell, Mats Øverby won the IBU Cup overall last year but not only did he not get the bonus spot for the IBU Cup winner that is automatic for the first two World Cups (that used to be specific to the winner but is now just for the nation, as often the IBU Cup winner ends up being a journey(wo)man who is there-or-thereabouts but not getting promoted season-long as dominant athletes at the IBU Cup tend to get promoted. Jenny Enodd on the women's side is a perfect example of this, there are plenty of experienced athletes who have got stuck at this level serving as gatekeepers of promotion, such as Lucas Fratzscher, Nadine Horchler, Elisabeth Högberg, often going well at this level but not successful enough at the World Cup for the team to prefer them over a younger talent if it's a 50-50 pick), but he has only got selection at one IBU Cup weekend so far this season - Øverby is only 24, though, so not really falling into this category (you could argue that, of their current top IBU Cup guns, Sivert Bakken might be in danger of it, at 26, or Sverre Dahlen Aspenes at 27 and Sindre Fjellheim Jorde at 28 - yes, Dale-Skjevdal is 27 but he also has proven World Cup pedigree that those others don't) and Martin Nevland was 3rd on the IBU Cup and is only 23 but hasn't even got an international start this year.
That's without looking at the former successful juniors that are now no longer able to compete at the junior level (even if Norway took up their invites at the Junior World Cup) but are stuck at the Norgescup this year as well due to the logjam of competitors, such as Einar Hedegart (who scored a World Cup top 10 in the Cross-Country at Lillehammer), Trym Gerhardsen and Vetle Rype Paulsen, who would be at least strong IBU Cup competitors for pretty much any other country, if not at least rotational World Cup talents.