Habits were in their origins the dress of the day for widows or poor women. Orders like the Dominicans and Franciscans were clothed in monastic attire. Those original outfits never got an update until Pope Pius XII suggested to women religious that they modernize their clothing. The women listened to the Pope and the rest is history.
There is no ONE official dress for women religious because of these origins. Clothes do not make the woman who she is....her dedication to her Community and its work are the important things to use to measure her dedication. Many women give their lives to better those of others in myriad ways and that's what counts. Police detectives wear no uniforms when on duty and that takes nothing from their dedication to their work.
The longing for the "fifties" and the "good old days" does not further any religious endeavor. We live in the present.