If you're reading this, you probably already know that the Atari 2600 was certainly the most popular video game system of its time. It suffered from poor hardware (it doesn't even have a graphics processor), yet it was a huge success and people continue to play its games. Why? Variety. If you pick up two randomly selected Atari 2600 cartridges and play them, you'll almost certainly experience two totally different games. You simply can't say that for modern systems.
The lack of a graphics processor and the tiny RAM (128 bytes) and ROM (4k without bank-switching) make it a real challenge to program. Of course, hobbyist programmers love a challenge, and new games continue to be made for the 2600. In fact, it's probably the most popular classic console among hobbyists developing homebrew games. The only really close competitor to the 2600 is the GCE Vectrex.