Think about it. He's no spring chicken. He's paid his dues in life and can certainly do without the aggravation.
He would be inheriting a splintered country, more divided than ever before (but Trump is still nominated for a [cough, gag] Nobel Peace Prize).
He would be inheriting a country where Trump took all the credit for some of the groundwork by the Obama administration to get the economy headed in the right direction (economy lag time... economic indicators... and all that... if anyone cares to look).
And NOW... probably poised for some inevitable consequences of some Trump bonehead moves that may have THEIR effect on the economy sometime during the coming year.
Trump would NOT ride quietly off into the sunset. He'd remain on the sidelines, now as a disgruntled former President.... criticizing Biden the minute the guy put his feet on the bedroom floor every morning in the White House. Undermining every single decision made by Biden, and egging on his angry supporters to do the same. He would make life miserable for Biden, but now not just as a blowhard pest of a man who just won't go away... but as a former President, with all the power that unfortunately comes with it.
Trump would openly gloat over Biden's (and by extension the country's) misfortunes... and anyone who cares to dispute that statement seriously needs a reality check.
So all things considered..... why in HELL would anyone, especially a soon-to-be 78 year old man, want to be POTUS??