Sacrosanct
Legend
I play and run Adventurer's League. So, if it's in the official game, I have to deal with it. Streamlined game design is not just prettier, it's easier from the consumer point of view.
More to the point, and I don't know if this is an issue elsewhere or just in my area, but AL DMs are in short supply. So by the nature of AL, they have to be DM friendly. If you have too many official options, it's hard for DMs to keep up with everything because a DM should be familiar with everything the players are doing or will do. It's just part of planning an preparing. So if you have something like the AD&D UA stat generation and a player saying "Well, it's in the official book, so you have to accept it." I'm pretty sure most DMs hated that stat generation method. Only monty haul munchkins loved using it*. That dissuades people from DMing if they are forced to include something they don't like. I think that's a key problem between making something official, and making it 3PP for your own personal gaming groups.
*for those not familar, you basically rolled 9d6 take top 3 for your primary attribute, 8d6 for secondary, etc. So you were pretty much assured to have a bunch of 18s and 17s for your stats.