Revenge

Here's an example:
ST6 kills bin Ladin. Americans celebrate his death. Americans look bloodthirsty, shallow, and like they don't care at all about international agreements. We may have won a national victory, but around the world, we look like fools.
Yes, al-Qaeda may have lost a very valuable asset. But we lose more than we gain. We already have little enough respect around the world. Why lose the little that we still have?

At this point, much of the rest of the world, particularly the EU, have already proven themselves to be amply useless in the grand scheme of things, so really, who cares what they think. The worst they will do is pass some sanction that everyone else in the world will ignore, just like all of their other decisions.