Here's why:
* The word itself is "italien", which is a masculine noun.
* Adjectives in French generally agree in gender with the noun they modify. So, if you're talking about a "Italian person" (un italien), you would use the masculine form of the adjective. However, if you are talking about an "Italian woman" (une italienne), you would use the feminine form.
Here are some examples:
* Un homme italien (A Italian man)
* Une femme italienne (An Italian woman)
* Le cinéma italien (Italian cinema)
* La cuisine italienne (Italian cuisine)