Why wasn't Jefferson Davis executed for High Treason?

No. The British had outlawed slavery long before the American Civil War, and even had an Atlantic squadron dedicated to ending the slave trade (the West Africa Squadron, established 1808). In the aftermath of the events dramatized in the movie Amastad, the Royal Navy in 1840 shelled and destroyed the Spanish citadel that was being used for exporting slaves (after first storming it and freeing the slaves held there).

We need some guillotine doors for these dogs.

Ooooooo…nasty!

Ooooooo… more nastiness!!

I realize that … I was referring to the executions cited.

There was widespread sympathy and support for the Confederacy among the aristocracy of Great Britain (and France). Part of it was economic-the South was a major supplier of cotton. Part was pure politics, that Britain’s interest made sure that no other country got too strong just in case there was a dispute and the United States was growing rapidly. Part of it was class driven as British upper class more identified with the Southern instead of those grubby Northerners who made their fortunes in business instead of the approved old fashioned way-inheritance.
There were a few blunders along the way such as the Trent affair before cooler heads prevailed. But what ultimately won the day to keep Britain and France neutral wasn’t the Emancipation Proclamation. It was a new generation of warship: the ironclad Monitor. Great Britain realized that it’s navy was suddenly obsolete, including
it’s more primitive ironclad Warrior. While the Monitor was a coastal vessel, certainly ocean going ones could be built.

Britain did outlaw slavery earlier and spent a lot of effort congratulating itself for it, glazing over the fact that several centuries involved in it made her rich.

Judge: We are not going to execute you.

Defendant: Whew!

Judge: We are going to execute… your head

Defendant: NOOOOOOOOOO!!!

In what respect was Robert E. Lee a statesman at all after the war? He was president of a college.

Another factor was that Davis wasn’t particularly guilty. He hadn’t been a major voice in pushing for secession in 1860. The fact that he was regarded as a moderate was one of the main reasons he was chosen as President.

Statesmanship does not necessarily (or even readily) reside in public office. Lee testified before Congress, corresponded with Southern leaders, made speeches, and arguably influenced the tenor of the Southern response to US policy after the war. Things did not go as he wished, on the whole, and maybe that’s well enough, but he tried to be a moderating influence, and succeeded in part.