Because management notice nowadays that some fans are supporting the group as a whole or as a team instead of the very common individual members only. They decided to implement the pennant race system this coming January and the Drafting Event today is the first step towards it. There will be two training system: the common kenkyusei (girls who passed the regular AKB autidtion) and the new ikusei (girls who will be pick at the draft).
The said system will be like the AKB's famous senbatsu election but this time the battle was between all of the existing teams in the 48 fandom. Management will rank who is the best/most popular team at the end of the time frame which will be based at the theater reservation/application. This is the management way to finally introduced the full 48-family's concept to the public because most people don't know the existence of Teams and think that AKB is only composed of the senbatsu members and not aware of the stage songs.
This is fun. 48-family has always something new things or gimmicks to keep the fans interested about them I just wondering if they can release an A-side single which is composed of a team only for example AKB48 Team-K 1st single. But anyway this is fresh and if this gimmick succeed I believe a new revolution will come to the fandom to keep them alive hahahaha