In a nutshell: corporate greed. The only part of the game that was live service was the paid cosmetics.
At launch, their entire idea of more ‘content’ was just visual cosmetics. If you look at their communications at the time it will all make sense.
They constantly referred to an internal ‘live service’ team separate from the rest of the game, and that team was effectively the ‘cosmetics team’.
People talk about contractors, but this was the real problem. They thought they could get away with barely adding any real content and selling tons of cosmetics.