"why refer to them as bars and not measures?"
We could turn that question around and ask "why refer to them as measures and not bars?" It is a terminology thing.
It appears the US prefers measures full of quarter notes and eighth notes while the English (and at least some others) prefer bars with crochets and quavers.
Musicians and nightclub DJs need the tighter control of specifying tempo as beats per minute. Dancers are generally more worried about choreography to fit into several bars/measures so have traditionally specified tempo in bars per minute.
So, why is the famous song titled 'Beat Me, Daddy, Eight to the Bar' and not 'Beat Me, Daddy, Eight to the Measure.'
