Having been in World 63 Germany since inception, I noticed periods, over time, when there simply would not be very many new young German players entering the system. I always figured it was because the sim measures how deep the player pool is at any given time, and that there may be an algorithm which adds new talent as needed.
Also, in our world, we began with Germany, USA and England. Belgium was added in Season 4. So there was a period there when all the German, American and English players were in mid career, and all the hot young talent was Belgian.