But does he fear taking direct action to subvert government more than he fears prison? Because he is staring at possible prison.

Maybe - but by the time we get to 2029, nearly all of that will have resolved. The federal cases will be gone. If Trump wins in 2024, he will certainly have DOJ dismiss all the federal cases and grant himself a pardon of all federal crimes. His state criminal cases will either be done (like NY) or delayed for four years, which will have crippled them. He'll also have had four years to try to get the Georgia state board to give him a full pardon, or for the state legislature to pass something to remove his potential criminal liability.

So in 2029, his odds of going to prison are much lower than they are now (or if he loses in 2024). Certainly much lower if he just steps down than if he tries to convert the US into a dictatorship with Trump as President-for-life. That's an insanely high-risk endeavor, and if it fails he's guaranteed to go to prison for the rest of his life. That's a much bigger risk than he would face in any of his other criminal matters in 2029, so he'd be making matters worse for himself than just stepping down.