From FB group
James Short
What the Game makers did was buy windowless 27C64 EPROMs, for example. That makes them cheaper, but you can only program them once, because they couldn’t be erased. Once they had finalized the firmware, they had it mask programmed into ROMs at the chip factory, because they could order enough (10s of thousands) of the proms to make the price very cheap.
And then we paid $30 per cartridge for them, and they became rich overnite. 😬😱