Just look into climate, topography, and available crops. Large part of Western, Central, and Eastern Europe is flat. Really flat. It is often referred as European plain. This land was extensively farmed since the late antiquity, and the population of European plains was much higher in the peak of the middle ages than was during the Roman Empire. The European agriculture utilized a deep plough and only certain cereals and products could be grown there in that climate. Much of the modern European food has an origin in a New World. Therefore, on really flat terrain, extensive use of the plough, and a high consumption of dairy products was not that suitable for a terrace farming. Could not imagine how it would work in such agriculturally productive areas like were Low Countries or France.

Mediterranean basin has a different climate, with much drier weather, and was extensively cultivated with specific crops since antiquity. Irregular rainfall would make the terrace farming unreliable. The primary crop in the southern warmer areas of Mediterranean were olives, which was the biggest cash crop for Greek cities, and southern Italy. Second crop cash was of course wine. Many other crops in Europe did not appear until later, either during Crusades or Ottoman times. The existing medieval agriculture survived in Europe for over 1000 years and it was due a climate rather suitable.