Explanation: Olive oil was a vital foodstuff to the Romans (and many other Mediterranean peoples). Everyone ate olives and used olive oil - even the infamously callous cheapskate, Cato the Elder, advised giving olive oil rations to slaves. Olive oil simply could not be done without!

Butter in a Mediterranean climate before the invention of refrigeration can go bad... very quickly. So butter never really caught on in the Mediterranean, despite having no lack of cattle or lack of interest in dairy (cheese was another major foodstuff of the Romans).

For this reason, Greeks, and later Romans, would associate butter-eating with those strange northern BARBARIANS! How uncivilized!