Like a lot of foods, the taste is a result of where they are grown. What got me started on my quest for an olive oil from anywhere other than Italy, was my daughter-in-laws family. They come from Albania which is north of Greece. Her mother suggested I try Grecian olive oil. She said it is not as bitter as the Italian. I find that a lot of the foods and recipes of Italy are based on bitterness. When I got into a conversation with her she agreed with me about the bitterness. She said it may have to do with their lifestyle. So many of their little villages are located on steep hillsides, their areas of growing foods are on rocky earth. They just have never had an easy way to make a living. Specially in the areas of the volcanoes. And then add their politics to it, it just makes their lives a bit more difficult and uncertain.
I grew up in an Italian part of Boston. We had a great influx of Italians after the war. We had a POW camp of Italian prisoners out at Wood Island. When the war ended most of the prisoners chose to stay here. We also had an Immigration Processing Center, akin to Ellis Island here. They processed immigrants coming from Italy. So when I would go to the homes of my girlfriends, I would hear all the stories of how hard their lives were in Italy. There was always a story to go with the food and why it was made the way it was. It usually was because the Blessed Mother was not looking down of them for some reason. They chose bitter foods because they grew in the wild and were the only thing available. They developed a taste for bitterness.
Greece didn't have it as difficult during the war. They didn't have it easy, just not as hard. And their soil is sweeter than in Italy. As a result, their olives are grown in sweeter soil.
Time to end this lessonn in history. I go on and on.