My guess is that they are in response to DM's who don't trust their players
Players are people. They make math errors. They misunderstand phrases in the rules. They only read as far as they find a magic item description interesting and then stop. There are plenty of reasons to confirm a player's interpretation of anything rather than simply accepting it at face value, even if you otherwise trust that player.
(Edit: I believe the famous phrase is "trust but verify". It's good advice.)
Also keep in mind that other players don't have this power -- if you've ever been a player in a game being ruined by someone who obviously was misintepreting a magic item ability or had clearly forged an item award and watched helplessly as the DM did nothing to correct the error, you might have a different idea of the DMs role in keeping AL games entertaining and fun.