What you forget is that in making this drastic hange in an official rule book, it will change how my table will have to play in AL context. The PHB+1 will soon become PHB+2 and quite a few players will balk at a notion that I might not allow "x" because it is in Tasha... Even personal games will be affected one way or an other as arguments will spring up when a new, or an old player will want to play an odd class/race combination with no drawback because Tasha allows it. I can see young DMs having to argue with said player just like I did when a player wanted to play a ninja in my campaign ecause it was an "official" class with OA. Same in 2nd edition with the complete book of "x" with kits, or 3.xed with the class books. Or 4ed with PHB2+. A DM do have the right not to play with some books when they are not core. But when they are core books as Tasha will be considered, it is hard to justify. The younger the DM (experience wise) the harder it will be.