Investors happened. They drive a constant demand for increased profits and growth from their investments. Once you reach the threshold of "everybody and their grandmother has a copy," the only real way to get more money is by releasing paid DLC or some mechanic that convinces players to convert real money into an easily consumable in-game resource.

On that note, indie games are the way to go. The amount of free content that keeps being added to 5 year old games like Stardew Valley and Terraria is crazy.