When you buy a painting, a book, or a horseshoe, the creator’s labor ends the second you buy it. The object just sits there, existing on its own. Software doesn't do that.
Because of the reality of how technology works, code doesn't just sit in a vacuum forever. Operating systems update, hardware architectures change, server protocols shift, and security certificates expire. If software is left completely alone, it eventually breaks (a concept known in IT as "software rot").
To keep a game, especially a modern one, functional and playable for a decade or more, engineers have to actively maintain it. They have to patch it for new operating systems, migrate server infrastructure, and update APIs.
So, when someone pays a one-time fee of $60 and demands that their software remain perfectly functional until the end of time, they aren't just demanding ownership of a static object. They are demanding that a team of engineers continuously update, patch, and maintain the infrastructure for that code indefinitely, without ever being paid for that ongoing labor.
That is what "engineers to work for you for free in perpetuity" means. Pretending that software is a static object like a book ignores the reality that demanding permanent functionality from code requires perpetual, unpaid maintenance from its creators.