Is just because brand loyalty. You see, Nintendo has been milking on his older consoles for the last 30 years. The constantly remind every of their consumers how good they were with the NES, SNES, N64 and they re-release their games in every single of their consoles, so you should buy their games. Thats why 99% of this board always discusses only NES and foward games.
Atari has been dead like 25 years. Also their only good console is from 1979. On top of that -i never understood why- the amount of Atari collections in the market is VERY low. For example SNK has a Metal Slug collection in every single device that runs faster than 500Mhz of processor, even if it is a fucking blender. But Atari never did that. They even outsourced the flashback series which is stupid.
And finally -something that many people here wont admit- the graphics are very crude. I like them because i got an Atari in the early 90's and it was my first console, so i think they are ok, but many people here actually get pushed away because their characters look like dots or sticks.
Oh and the atari controller is not a good controller for today standars. Even back then i hated it because how fragile is, and considering how much skills and timing the games requires, the controller doesnt hold up to the challenges you have to confront.