As blueparrot says, it won't happen anyway, but we have a moral duty as a wealthy nation to protect our citizens AND citizens of other countries during a global health emergency. Would you be happy with us vaccinating completely healthy 25 year olds whilst a 65 year old from Italy or Austria with health conditions can't get near a vaccine because of short supply? Whether that's a consequence initially caused by an EU fuck up or not, it won't help and human lives would be lost if we took your stance.