They sold at least 5.92m copies, which amounts to roughly usd177m revenue(roughly usd124.32m after steam cut), and with the playerbase tanked from 2.1m peak to 682k peak in just 14 days, they can survive for a veeery long time with that kind of money.
Usually that affects businesses that either provide an online service, so their costs spike massively, or are selling physical objects where demand so far outstrips supply that customers leave entirely for something else.
A single player / selfhksted multiplayer game like this is much less vulnerable to those aspects.