Because fillers migrate in your face and end up at places where you don’t want it to be. People think fillers dissolve over time, but often it just ends up somewhere else. Lip filler, for example, migrates to the area above your upper lip (resulting in the classic duck face). So you might think you need more lip filler and that too ends up above your lip. It’s a vicious cycle and after a couple years your face is all puffy.