That is a common misconception Pop, I outlined this above, but ill quote myself for reference.
DCUO = free
FFXVI = Global sub
ESO = Global sub
SWTOR = Global sub
Runescape = Global sub
Lost Ark = Global sub
Eve Online = Global sub
Conan = Global sub
And then every other multiplayer title out there eg. Battlefield, COD, Rust, PUBG, R6, Minecraft, Overwatch, CS, Valorant… The list goes on, basically every single game.
None have issues with regional trade, price differences, taxes and currencies, its a complete fallacy that only Blizzard and only WoW have issues with this. They just either havent gotten around to fixing it, or dont want to. Its demonstrably false that MMO’s have issues with this, or any multiplayer games for that matter. Plus, huge AAA corps like ActiBlizzard have gigantic legal teams on their books 24/7, they can work around any legal issue they want.
With regards to your sub fee thing, that is a valid issue, that has arisen most recently due to the strength of the USD $. However, its not difficult for them to lock an account to a region in terms of payment. Eg you must sign up with an account from your local region, so US players make US accounts, and therefore they are locked into a USD payment. This system exists in different forms already. Look at Steam, you cannot purchase a Russian key for a video game, its against the ToS and you will get banned for it if they catch you, because Russian keys are cheaper.
The issue may be currencies, but thats not an issue that cannot be fixed, as I demonstrated above. Every other game does it, but apparently WoW cant.