From the beginning of time, or at least the beginnings of art, there have been, broadly speaking, four areas of painting content--contemporary, religious, mythological, and formalistic. The earliest cave paintings were contemporary, dealing with current events or recent history. Religious works dealt entirely with various deities. Mythological works probably grew out of Greek religious content but came to prominence in Western art long after they had lost any religious following. And finally, in this century, came formalistic content in which the subject of the art is art itself. At various times though history, several of these areas have dominated art. If we count painting as having come into its own during the Renaissance, then we find much of it religious, with mythology running a distant second but gaining ground. With the Reformation, contemporary content slowly began to dominate. During the eighteenth and nineteenth centuries, mythology replaced religion and contemporary subjects as the artist's subject of choice. Since Impressionism, contemporary subject matter has seesawed back and forth with newly important formalistic concerns while religion and mythology in art became practically non-existent. That's a brief, breathless history of art in one short blurb.
Today, while there, in fact, continues to be a small religious presence in painting, mythology is dead. Sandro Botticelli is credited with having painted the first revival of mythological content since Roman times with his Primavera (1481). In modern times, Valentin Alexandrovich Serov with his The Rape of Europa in 1910 may well have been the last artist to seriously explore Greek mythology in painting. In between, there was the exuberance of Raphael's Galatea (1506), the careful, narrative choreography of Guido Reni's Atalanta and Hippomenes (1612), the Rococo fantasy of Boucher's Triumph of Venus, (1740) and the medieval longings of Edward Burne-Jones' King Arthur in Avalon.
That's not to say we have no taste for mythology today. Movies and television love it. But movies and television are well suited for telling the moralistic stories for which mythology is famous. It's entertaining, intellectual, adventurous, sexually exciting escapism. Today, painting takes itself too seriously for any such foolishness. Moreover, today, if artists even know or care about mythology, they are ill-equipped to deal with it visually. Painted mythology demands a familiarity with the subject matter that most people (including artists) simply don't have. Or, it demands the ability and willingness on the part of the painter to visually expound upon the antiquated arcanities of the subject which few if any artists possess. All of which would be of little consequence except that with religious painting seemingly following the same path to oblivion, we find relegated to benign obscurity fully half the traditional subject areas of the painter's art. And that's both sad and frightening.