Part of the reason is that the Arab/Moors once occupied Italy under the Arab Caliphate from 645 AD - 885 AD. Even though Italians reject this ancestry because the Arab/Moors raped and pillaged their way into power, there is a strong genetic presence of Arab/Moor ancestry.
The original people of Greece and Italy are both Mediterranean and Alpine Caucasian ethnic groups. Arabs are Mediterranean Caucasians. Thus the original Italian ethnic groups (purely caucasian) were already closely related to Arab ethnic groups via human evolutions. This can also explain their similarity in appearance.
Greeks also mixed with Arabs like Lebanese and Egyptians during ancient times. The mixed bloodlines exists inside Greece as well as in Lebanon and Egypt. So, subsequent Arab ancestry could have been brought into Italy when the Greeks arrived there. Perhaps there were Italians who immigrated into Greece as well.
The Arab/Moors also occupied Turkey and Armenia which could also explain the similar phenotypes. Those countries also reject this part their ancestral heritage and have attempted to totally write it out of their history books and the Internet. You will mostly find history references to Islam in Italy which existed under the Arab Caliphate from 645 AD - 885 AD.
The definitions of Arabs and Moors, during this time frame, are interchangeable.
However, other bloodlines have since been introduced into Italy since Arab/Moor occupation, such as Nordic bloodlines from Ireland. There was once a definite phenotype difference between Italians living in the North and those living in the south, as Southern Italians were known for being darker in hue - some of them bearing strong resemblance to the dark Moors who once occupied the country.
There is an argument that Nordic populations were deliberately encouraged to immigrate into Italy in order to lighten the population. This same practice was done during the colonial era in North Africa when the Berber population had become, generally, very dark and people from Britain were brought in to lighten up those regions. The original Berbers were Caucasian, but the populations had undergone heavy interbreeding with those of recent/promiment sub-Saharan ancestry for some centuries prior.
**note: Arab royalty from countries like Morocco and Jordan have fairly recent North European ancestry
Countries in that part of the world have intricate histories and population migration patterns that cross over into one another.
You should look it up, you'd be surprised by the connection of culture, language and bloodline.