In part - the entire game takes only a few hundred megabytes and can be played on anything but a toaster.

But it's also the great concept, the simplicity, the legacy, the compatibility, and the insane amount of mods able to significantly alter your gameplay or visuals.

As a simple but deep and visually appealing sandbox, it managed to capture many audiences - creatives of all kinds, replica makers, casual survival players, automation/industrialization fans, computer enthusiasts, and many more.

It also helped that Minecraft is extremely easy to pirate and also long-lived, making many enter it as pirates and purchasing a copy later on (or staying pirates and still generating a lot of content for the community).