Also a possible reason why others don't use or like the AT in the game is because in gameplay, it doesn't act like an actual one. For example, a typical AT would change its behavior by upshifting or downshifting depending on the input made in the throttle. However, in gameplay, the AT behaves much like a MT, where it doesn't upshift at all nor drop the RPM down when you let go the throttle and doesn't downshift as you push the throttle down when it should. You need to wait for it yet to reach a certain RPM just to do those shifting. So it's just essentially a MT controlled by an AI, that the engine speed would always match with the speed of the car while running.
The real AT in the game are the cars that have only one gear, those with CVTs that when you use, only indicate 'D' in the display and they somehow really act like one because the RPMs would drop when you don't press the pedal at all. I don't know if all those with CVTs in the game act like this but I tried it with the Mitsubishi i Concept in stock tranny and it certainly behaved that way. Maybe PD fixed this in GT Sport, which I haven't played yet because I don't have a PS4.