It’d be wasted breath, really. Trump will never step down, because he’s trying to remain out of prison. If he loses, then there goes any chance he had at pardoning himself for his numerous crimes. So he’s not only the far and away favorite Republican candidate, but he’s also highly motivated to stay in the race for personal reasons. No appeal to his sense of patriotism will work to get him to step down because he has no patriotism. He’s in it for himself and himself only.
Biden, on the other hand, is just the default Democrat guy because he’s the incumbent, and the party figured that’d be enough to win, and so haven’t been trying very hard. And that has everybody terrified, because if he loses, then we get another 4 years of Trump, and probably never get to vote again. Basically, people are calling for Biden to step down because the stakes are way too high to fuck around.