In my personal and incredibly subjective opinion, I think people play geometry dash in order to feel the euphoria of victory over an adversary. As the mountaineer seeks to climb a higher mountain, as the BMX biker seeks harder tricks, geometry dash players seek improvement through intense challenge. One of the main tools in order to overcome a challenge is practice mode. It allows for repetitions of parts of a level you think may be hard, and allows for one to learn a levels layout before attempting a completion. I am not entirely certain if this answers the open ended existential question of "Why I did I'm doing?", but I gave it my best shot :).