... is because literally any other fandom can do the same thing. ARMY doesn't have a super-secret advantage over any over fanbase. They have learnt with time how charts worked, but that's something that every fanbase can do. And they do it, just not as efficiently as ARMY. Everyone can fund purchases. Everyone can organise streaming parties. This just asks for some dedication.
Do you want to call BTS success fandom-driven ? Alright. But ARMY is just playing the game better than other fanbase, and other players start throwing a tantrum because they are furious to not have the same amount of success.
Instead of crying over ARMY wrecking the game, maybe other fanbases should wonder why they are the only ones able to do so.