Some months back, I looked a bit into Hello Games' financials, see
this post: as it turns out, the power of massive marketing (financed by Sony) was such that they made enough money that even if all income was cut afterwards, they could have kept developing the game for over ten years. I don't think that all those copies sold were based on the state of the game at launch, because really, it was quite the debacle.
So, sure, they developed the game quite well over the years, but they did so at practically zero financial risk, and an original reception that was poor enough that they could really only go higher. It's a good thing the developers kept at the game and improved it over all the years, of course.