I am just a small fish internally in Elite, so don't take my word as the official word of the alliance.
That being said, we also took a few recruits in the hope of training them. Probably not as many as ATeam, but still, we take a few each game. It's a gamble. Some will succeed, some will fail. That's a part of the risk.
Both ATeam, us, and a few other alliances, have a few very, very, very good players, who always score high. The temptation would be huge to kick everyone else from the alliance one day before the end of the game. That would be gaming the system. Imagine, we do that : the standings would be :
"Winner, Elite, 3 members, 2500 points. Second, ATeam, 33 members, 1800 points". Elite was 28 members 2 days before the end of the game.....
Does it make sense? nope
Does it risk to happen? Well, most other alliances would do the trick, too.....so alliances would be empty the last day, bar the best players.