Why?

This means Britain will actually have one trade agreement by the time it leaves the EU.

"This is a great example of how current US foreign policy means a loss of soft power all over the world"

Agreed, it does seem very short sighted. Once a system is in place, and it works, suddenly its very easy to apply that system to any other regime where the US doesn't agree with the rest of the world. Plus what's the point in 'rogue' states coming in from the cold, if the US are going to renage on their agreements.