Except you're missing the point. The Supreme Court doesn't decide the qualifications to initially get on the ballot, the state does.
Whether or not he's qualified for the ballot is determined by the state officials, who don't need a conviction to disqualify him. This is awfully inconvenient for Trump, as instead of Cawthorn's case, where the Free Speech for People brought the case against the decision of the state officials, Trump would have to start the case and fight his way through appeals - while fighting 3 felony cases in different courtrooms at the same time.
This means that if state officials disqualify him, he has to file the case, and wait for it to either resolve or go through the appeals process, likely all the way to the Supreme Court just to get on the ballot. When you consider the timing, it's highly likely that the case wouldn't resolve or make it to the Supreme Court until after the election. The fact that Trump cost GA a senate seat, and dragged Raffensberger through the mud makes it more than a bit likely that GA election officials will disqualify him, as some of those same people are the ones who provided evidence for the indictment.
The other element comes down to the Supreme Court itself. It's loyal to Trump, but loyal enough to condone open rebellion at the cost of its own legitimacy? That's difficult political calculus for any institution of government, much less the Judical Branch, which has no enforcement arm and no legitimacy beside what Congress chooses to give it (the Constitution only states that a Supreme Court be established, and leaves it to Congress to establish it, which they did with the Judiciary Act of 1789 ). Roberts is already on the line, and a decision like this would prompt Congress to act on the ethics conflicts he's been desperately trying to sweep under the rug.
Right now, it's most convenient for almost every GOP official to have Trump go away. Yes, they were happy to ride his coattails into power, but now their power is directly threatened by his incompetence. On top of which, he's destroyed the party's finances. A lot of establishment Republicans are ready to throw him under the bus, and this may be their opportunity.