Not everyone wants the Tasha's cauldron additions in their 5e game - it is not core 5e, but something you can *elect* to use. BG3 was only ever referred to as a 5e game - and "the definitive 5e game" (or some such) at some point - not 5.5e, or DnD One or whatever the next iteration is (which I will be skipping). When I shelled out money, years ago, that was what I was expecting - not the 5e+/Larian hybrid we're seeing now.
If the game is designed around these changes/additions, even if a player tries to emulate the actual core 5e rules and experience, every other system in the game, including all the enemies you see, action economy etc, *will* use these changed systems. So you are forced to engage with them.
