The YOG is a smaller roster (9 forwards) so there's less opportunity to make the team. Namestnikov also wasn't at the USAH Select 15 Player Development Camp last summer, which served as the primary evaluation event for choosing the YOG roster. USAH doesn't prepare much for the tournament. And lastly, player evaluation at the 14/15 year old group isn't exactly a science. Things change quickly. Just look at the previous two USA YOG rosters. The '00 team didn't have what ended up being 2 of their top 3 NHL prospects on it (Joel Farabee and K'Andre Miller), and guys like Bode Wilde, Zac Jones, Alec Regula, etc. weren't there either. The '96 team didn't have Kyle Connor, Alex Tuch, Christian Dvorak, Brandon Carlo, Ryan Donato, Conor Garland, Sonny Milano, etc. The '96 team was also missing Dylan Larkin, but he was injured.
I don't know who Namestnikov will officially represent in the future if he's good enough for that to matter. But he was going to try out for the NTDP at the evaluation camp that was supposed to start tomorrow. Rumor is that the camp is cancelled and they may be naming the team soon. So if he gets an offer and accepts, it'll be USA Hockey.