According to Bloomberg, Hollow Knight has sold over 15 million copies.
The info was shared by Team Cherry with journalist Jason Schreier, who wrote an article explaining the delay for the sequel, Hollow Knight: Silksong, which finally got a release date: September 4th.
Essentially, the delay stems from the team not wanting to expand or alter their development approach. As the sequel’s scope grew larger, the production timeline naturally extended. There was no controversy—just repeated instances where projected deadlines proved unrealistic, requiring additional development time.