What possible reason would he have to do that...? If he wins, he gets off scot free. If he loses then he'll claim that he won and is being suppressed for political reasons and then get of scot free.
If he were a traditional candidate, the answer is that the party needs to have a candidate who not only can win, but also supports candidates for lower level elections. A traditional candidate would step aside and nominate someone to take their place. Not sure if the GOP convention rules allow it, but they could possibly even direct their delegates to go towards someone else.
Since Trump is a narcissist who doesn't even get why downstream elections are important for building a political base of support, he'll of course ignore this.
In the event he actually gets incarcerated, if he were to win the presidency he could sue claiming being locked up interferes with his constitutional duties as president. I think I know what this Supreme Court would decide on that
This Supreme Court has not always been friendly to Trump, nor his cronies, nor conservative causes. Their rulings are all over the place regarding politics. Here's a pile of liberal wins.
If you have the pile of links why not post them? This is just a screenshot of truncated headlines masquerading as a source.
One of the headlines is "Samuel Alito Is Mad You Can't Be Bigoted Towards Gay People Anymore." This could be an article about the current conservative supreme court protecting the rights of gay people, or it could be an article about how the supreme court is planning to strip rights from gay people. I don't know because you didn't actually post a source, you posted a screenshot of a list of truncated headlines.
We should not speak of Trump pardoning himself as if that's a legitimate power he would have, rather than a batshit crazy end run around the obvious intention of the Constitution.
And in any case, he's been convinced to state crimes, and there's no legal theory to support the idea that he can pardon himself or anyone else for state crimes.
He won't need to, it'll be his "independent" department of justice calling the shots. Sessions and Barr did everything in their power, without committing actual explicit crimes, to keep Trump happy while they were in charge.