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

Question

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.

Answer 1

In general, both Adeptus' and IcyFire's answers are correct. Specifically, the flanking rule makes positioning on a map more important since some class abilities are based on having advantage. This applies mostly to the Rogue, which already has a way to enable sneak attack when an ally is adjacent to an enemy, so it would mostly only serve to cause another decision point in a player's turn while they seek the best way to get advantage while not provoking attacks of opportunity from other foes. All of which takes time. Multiply that by 6 players and each round is going to take a bit longer trying to make that decision, every round in every combat. Ultimately not allowing flanking makes the game simpler and speeds up combat.

Source: I am the Community Manager for the D&D Adventurers League, Robert Adducci

Answer 2

Because the DMG wasn't finalized when AL started

I did a bit of digging, and found this article from December 2014: (excerpt, emphasis added)

Rules contained in the Dungeon Masters Guide may be permitted in future storyline seasons by future versions of the Player’s Guide. Until then, the Dungeon Masters Guide can only be used in D&D Adventurers League games to look up magic items and for general advice on how to run games. This rule was necessary in part because the book was still in editing when the D&D Adventurers League started.

This was written by Art Severance, who was Regional Coordinator for the US Far West region at the time that article was written (I'm not sure if he still is).

Variant gameplay rules cause inconsistencies between tables

The same article also states,

Just as the name implies, the D&D Adventurers League is a league game, in which everyone plays by the same rules, whether they always play in the same place or play all over the world. Characters within the League are portable, so a player who visits another area or moves there or who plays in an online game expects to be able to play his or her character there without having to make any modifications and without having to learn any local rules.

Allowing DMs to decide whether or not to use variant rules that modify gameplay, such as flanking, would mean that there would be "local rules," which runs counter to the philosophy that rules and gameplay are identical between AL tables.

Note that in V3.0 of the FAQ, nearly all of the variant rules that are allowed only affect characters, not gameplay. The one exception is playing on a grid, which I'd argue is a well-accepted, almost standard rule.

Answer 3

Part of the idea behind AL is to keep the rules consistent between tables. Looking at the variant rules able to be used, the only one not relating to character creation is Playing on a Grid.

From the AL FAQ:

Can I use the Variant and Optional Rules in the PHB/DMG?
The only optional or variant rules available for use are:

• Variant: Customizing Ability Scores (PHB)
• Variant Human Traits (PHB)
• Half-Elf Variants (SCAG)
• Option: Human Languages (SCAG)
• Tiefling Variants (SCAG)
• Variant: Playing on a Grid (PBR)

Without specific campaign documentation, any other variant or optional rules, such as Variant: Quasit Familiar (MM) are not available for use.

From the AL DM's Guide:

Rules for Dungeon Masters
The variant rules for “Playing on a Grid” in the D&D Basic Rules and Player’s Handbook can be used if you and your players wish. Dungeon Masters should feel free to use the Dungeon Masters Guide to help run games if they so choose. However, D&D Adventurers League play does not use any other optional or variant rules as presented in the Dungeon Master’s Guide.

Whether a game is played on a grid vs theater of the mind has little impact on tactics, but flanking makes positioning far more important, and has greater impact on balance.

So, if they allowed flanking in AL, it would have to be always in use for AL. This would make it effectively the default, which would make not using it the "variant".