Because all things are Atari. Gamer Sprybug over at AtariAge.com has taken apart the Nintendo classic Super Mario Bros and rebuilt it inside the Atari 2600. Right now, only a demo of World 1-1 is available, but Sprybug claims it might be possible to build 16 levels within the limitations of Atari 2600 programming.
From a technical standpoint, this is pretty cool. Especially the music, that has to be tricky on an Atari. That’s a really good Mario sprite, too.