In 1990, Atari (the original Atari) were in bad shape. So they sold off their inventory of old cartridges. O'Shea Ltd bought them. All 3 million of them.
They bought them so they could sell them on to you, the public. And where do they keep these millions of Atari cartridges? Why, in a 20,000-square warehouse carved from a limestone cave, of course.