Or get used as a sub, or played in a different position (like Kerr against Kille).
Youngsters, regardless of talent, blow hot and cold. They also lose the 'unknown' factor once teams work them out. Ojamaa is a great example of that. One of his advantages last season was teams hadn't matched up against him before.
This season, they know what to expect and set up to counter him much more effectively. It's easy for a young player to lose confidence that way.