Eh, it was probably switched off for all that time and only fired up again once Teletraan was online. Although... if that was the case, wouldn't the bodies scattered around the floor in the first episode all have slid off to one side? Unless the floor had specific high-grip surfaces, which I suppose could be the case. Ark crashes with internal gravity on, everything is pulled to the floor and against the grippy surface, gravity slowly fades over the next couple of centuries/millennia, there's not enough of an angle for stuff on the floor to start sliding.