For years, there was an agreement between the National Hockey League and the teams of the Canadian Hockey League forbidding any drafted CHL player under the age of 20 from playing in the American Hockey League. Any teenage prospect had to play for either their respective CHL team or in the NHL; they could not play for an AHL affiliate under they turned 20.
While this rule was frustrating at times, it was easy to understand why it was implemented. The CHL didn’t want to lose all their top talented players earlier than they wanted to. While those junior leagues are there to develop young players, the teams still need to make money to operate.