Atari made shit products that never sold, except for the 2600, the ST, and their 8-bit home computers. Aside from that, they also had stupid management, bad marketing techniques, and certain home consoles that they released under inconvenient times.
5600: Was not backwards compatible with the 2600, had horrible joysticks, and a library of re released games that you could have easily gotten on the 2600, so why bother?
7800: Arrived at the wrong time, and was ill-equipped to take on the NES.
Jaguar: Ill conceived effort to try and take on the SNES, Playstation, and the Sega Saturn. It had badly designed and faulty hardware, horrible controllers, and a small game library. This system literally destroyed Atari as a hardware company.