To put it simply - artists rarely use symmetrical balance in their work because it is boring. When something is perfect, it soon becomes boring to look at. This is why artists generally opt for something weird and unusual, and asymmetric, because it draws your attention to it more easily than symmetry. Other ways artists can create a visually appealing composition is by using complementary colors, for example, or shifting the center of a painting to the sides, or using negative space rather than positive, etc.