I dont think you understand the situation.
The DOJ cannot try a sitting president as matter of policy. If he continued the trial against policy then there is a good chance more judge delays and stays push it out until trump is president and he makes it go away, especially if he gets it dismissed with prejudice. If he drops it now it has the chance to be re-tried again when trump peacefully gives up power leaves office in 4 years time.

Legal eagle on youtube did a whole video explaining the situation in depth if you want a qualified explanation.

Leave my boy Jack Smith alone. He tried, the American voters failed him.