Yeah, Doge kinda nails it ("political"). Not only is it how well you ride in races, and which races, but it's also alot about who you know. Not necessarily you directly, but for instance, your coach. Maybe he has a good reputation in the community, and does he know the right people. He can then recommend you to them, they take a look, and like what they see, and give you a call, maybe an invitation to a team ride or camp or something, where you then prove that you have the goods and attitude to belong. And attitude is very big at the youth level (U23). Sure, maybe you have the talent and maybe even potential, but if you know everything, no one else will want to waste their energy trying to teach you.
Now, it's also possible to do this without knowing people/having a network of contacts. To do that, you just need to show up to the races that prospective "special teams" show up at, and then you spank them. Their coach/director will then take notice of you. But unless you have natural talent to beat them at their game AND a hard work ethos to develop it, this is much, much harder.