In most events the best athletes competed. Also it is a very nice chance and a Great experience for all athletes who are present. Many of them will never have a chance to medal at senior level. I think it is a good idea to give athletes a chance to compete internationally as long as they aren’t good enough yet to compete at senior competitions.
I think only the following medal contenders decided not to compete:
Bol, Schwab, Miller, Healy, Vicente, Patta, Schulte, Ansah-Peprah, Dustin, Miron, Ingebrigtsen, Heyward, Baehre, Duplantis
Others like Knoroz, Kienast or Benfares didn’t compete for other reasons like injuries.