Goku is not one to give up. Ever. In fact, if you’re stronger than him, that just increases the chance he would want to fight you. And thanks to saiyan biology (or, hacks, as dbza kurillan puts it), a saiyan not only gets stronger and better as a fight progresses, he gets a huge boost (zenkai) in power everytime he survives a near death.
Lets face it, outright killing someone? Not in supermans character (unless we’re talking injustice, justice lords, red son or speeding bullets superman). And goku is too pure hearted and good to make superman want to kill him (nor would goku try to kill superman, dead people make horrible sparring partners).
Superman may win the first match, but that first match means nothing in the world of shonen. Shonen are all about surpassing limits which goku, as a posterboy should, exemplifies. Its all about how the last match pans out. Now then, onto bias.
Can we create infinite power from a finite source? No, but a superman fanboy would tell you superman has infinite strength, even though his powers stem from a finite source of solar energy.
Ok, how about this, goku when going ssj loses half his speed? What? It doesn’t make sense? Well according to the death battle (quoted by every superman fan in existence) his speed does drop. I mean honestly, how biased can you get? Deliberately fudging stats to make superman better, pfeh.
Superman fanboys are biased to fuck. Goku fans (fuck kakarot, im a vegeta fan) understand his character enough to know a fight is never over till one side gives up or dies, which goku wont.
Its just logic. Goku always wins in the end due to the characters of both him and superman.