Because the Americans want to tap dance on British banks' "asses".
I believed that there had to be something tangible that they could point to, other than just being "anti-British". It's a single entity rather than multiple banks, and it's I.ran, man.
The admittance now that they did break sanctions (regardless of "only" 300 or so) seems to show that this isn't completely unfounded, regardless of how appropriate it is to go public without a full enquiry.. But my stop kicked in any way so I no longer hold a position.