why don't they just run them over by dogs?

in ep 13 se 02 i was really pissed off. why the FU#$% didnt the gruop run over the deads with their dogs? why do they keep shooting them and not run away? the whole barn scene when they stand there and shoot the deads is so so stupid. the deads were all gathered in 1 place, why dont they just hit them back and forth with their dogs? why didnt the guy who drove the van just hit the gas when the father and son were onb the van's roof? why the hell did he stay there? stupid stupid scene, non logical at all.