I think you underestimate how much money they made in sales from the first year alone, enough to finance a reasonably run studio for years.

They likely have other sources of investment too, maybe publishing deals and private investors.

AAA developers and publishers have brainwashed people into thinking that MTX and subscriptions is necessary for continued development, its never been true it's onky greed.

They made a whole bunch of unrealistic promises before launch and were taken to court over it there only real defense was “we never said when we would be finished” so they might be sudo legally obligated to give every single unrealistic thing they promised or at least that was definitely how it started and nobody ever told them they could stop so they kept doing it.