Seriously? With the Grand Army of the Republicans occupying the entire South they were afraid they couldn't protect a court?
So... according to you Davis committed Treason, launched a devastating war, was responsible for the death of the better part of a million people; but they didn't put him on trial for logistical reasons?
And what makes you so sure they would they have tried Davis in the South anyway? They tried Henry Wirz in Washington. They didn't let the Constitution stand in the way of that.
Legal scholars at the time successfully argued that the government might lose on the merits. Most people understood secession to be legal before the war.
How about naming a few of them?
The U.S. Constitution says that treason will be tried in the location where it was committed. To be true to the Constitution, they’ve got to try him in Richmond. That’s a terrible spot for the federal government to try the president of the Confederacy. Not only because the jury pool is going to be tainted against the federal government but if you find people who are loyal to the Union, to try the Confederate president, there’s going to be the intimidation factor, especially for African Americans. That’s very real in the South after the Civil War.