Because they are so good at arts
Art cannot be defined with such words, it can only be defined with very precious words because art is like love, its hard to get but if you already got it... Never waste it.
Cause it's relevantly new type of art. Little over 100 years old. First movie was made at the end of 19th century. Other type of arts are old to compare with cinema/ movie making. For example, Architecture, Literature and Paintings are many thousand years old.
Modern art period starts 1860s to the 1970s. The term is usually associated with art in which the traditions was broken to create new styles and trends.