... see Minecraft, Rimworld, KSP as a few examples...
I mean, I agree that games should be moddable, but not from the premise of game profitability and popularity.
The highest-grossing video game franchise list is over-ran by products that are , pretty much, famously unmoddable.[0]
[0]: https://en.wikipedia.org/wiki/List_of_highest-grossing_video...