Why are banks and post offices open hours that everyone is at work?

Iv often wondered why banks, post offices, DMV's and other similar institutions are open hours that most people cant even get to them. The average work day is 9-5 monday thru friday and these institutions are open 9-5 monday thru friday. Just a thought..|||Because the average working hours, from nine to five, always applys to government and bank buildings just like everyone else.