What is the reason Adventurers League games don’t allow DMG variant rules, such as Flanking?

Our home games have been running with the Variant Rule: Flanking while playing on a grid. It came to a surprise to us, when we first played in the Adventurer’s League, that Flanking is not allowed in AL play.

I’m considering adapting the no-flanking rule in our home games now, and was wondering what comment or statements WotC have said about why they don’t allow flanking in AL. I am hoping to gain insight on which to base a decision.

To be clear, I’m not looking for an answer on whether I should or should not allow flanking (this would obviously differ from table to table), neither am I inviting speculation as to the reason why AL doesn’t allow it. I am looking for a WotC-representative (or similar) commentary on why the DMG rule variants, especially flanking, is not allowed in organized Adventurer’s League play.