All over the country banks were being robbed

不需要改动,all over the country 是状语,可以在句首、句中或句尾,放在句首有强调作用。
being 是表示进行状态,就是一直在进行,说话时都在进行。本来只是were robbed表示过去式和被动态就可以,但是为了强调进行状态也可以再加个进行式在里面。比如说：
I was just being teasing you all the time。
我一直都是和你开玩笑的,别当真。