I think the main reason is Trump's rampant narcissism. He cannot be seen as giving in to his enemies or being weak. But their has emerged another reason. He doesn't trust Mike Pence to pardon him!
Frankly, I don't blame him. The way he has treated Pence in the last couple of weeks could well encourage the Vice-President to withhold a pardon.
Trump tried to pressure Pence to break the law and throw out electors from states that voted against Trump. When Pence said he could not legally do that, Trump bad mouthed him to his MAGA followers. Then sent them to Capitol Hill together Pence, and the rioters could be heard chanting "Hang Pence".
Why should Pence pardon a seditionist who put his life in danger?
Here's a tiny part of how CNN.com is covering Trump's last few days in office.
Trump has been consumed by the unraveling of his presidency during his last days in office, according to people around him, which included a casual discussion among advisers recently about a possible resignation.
Trump shut the idea down almost immediately. And he has made clear to aides in separate conversations that mere mention of President Richard Nixon, the last president to resign, was banned.
He told one adviser during an expletive-laden conversation recently never to bring up the ex-president ever again. During the passing mention of resigning this week, Trump told people he couldn't count on Vice President Mike Pence to pardon him like Gerald Ford did Nixon, anyway.
Eager for a final taste of the pomp of being president, Trump has asked for a major send-off on Inauguration Day next week, according to people familiar with the matter, before one last presidential flight to Palm Beach.
But the signs of his impending departure are everywhere -- including right outside his window. Workers hung bunting Thursday that read "2021 Biden-Harris Inauguration" from temporary stands across from the White House North Portico. It was visible from his third-story residence.
Inside the building, Trump has been weathering a second impeachment and growing isolation from his onetime allies in sullen desolation. He has grown more and more worried about what legal or financial calamities may await him when he is no longer president, people who have spoken to him said, fueled by warnings from lawyers and advisers. He is weighing pardons, including for himself and his family, as he attempts to muster a legal team for another impeachment trial. And he is resentful of Republicans who he feels abandoned him in his hour of need, including the GOP leaders of the House and Senate.
Aides have pleaded with Trump to deliver some type of farewell address, either live or taped, that would tick through his accomplishments in office. But he has appeared disinterested and noncommittal.