Positive charges attract negative charges and vice versa. The way I understand it, is the electrons (which Thomson discovered) were first thought to be these miniscule points of negative charge held by these attractive forces within a positively-charged sphere-shaped cloud. Here’s the thing: electrons move, so Thomson’s thought that as electrons moved further away from the center of the atom, they actually concentrated portions of the positive-charged cloud into concentric spheres, like nesting dolls. The electrons are then more strongly pulled toward the center as they move further away because the sphere of positive charge between it and the center of the atom gets bigger and bigger. Thus the electrons revolve around the center.
Essentially, this gave rise to an orbiting theory for the electrons that are being continually pulled toward the center of the atom, thereby debunking the plum pudding! Unfortunately, this theory too was flawed, and we’ll learn about the succeeding theory which was the pre-cursor to what most of us grew up being taught in school!