“Why would they rob a 7-11?? That makes no sense once the pictures were released.”
To provoke the big final shoot out.
Maybe poor planning? Didn’t expect to be a suspect, had no firm bug out plans? Maybe they expected to die with their bombs but didn’t pull the trigger at the marathon? Whatever the reason, holding up a 7-11 and attempting to steal a car sounds like getting cash and wheels to run. In other words an improvised bug out plan.