First, Italy was the birthplace of opera. The first operas were written in Italy in the 16th century, and the Italian style of opera quickly spread to other countries. Italian composers and singers were in high demand, and Italian became the default language for opera.
Second, Italian is a very musical language. It has a beautiful sound and is well-suited for singing. The vowels are clear and distinct, and the consonants are soft and flowing. This makes Italian an ideal language for opera, which is all about the music and the singing.
Third, Italian has a long tradition of classical music. Italy is home to some of the world's most famous composers and musicians, and the Italian operatic tradition is very strong. This tradition has helped to keep Italian as the language of opera, even in countries where it is not the native language.
Of course, there are also some operas that are sung in other languages. In recent years, there has been a growing trend toward operas sung in English, especially in the United States. However, Italian remains the most common language for opera, and it is likely to continue to be so for many years to come.