A lot of people (including in this thread) seem to have this idea that art is about realism. The more a piece of art, or its components, bear a resemblance to reality, or the more technically difficult the methods involved in its execution, the more worthy it supposedly becomes as "true" art.
But this is totally missing the forest for the trees. Art is ultimately about indulging in a perceptual experience. The true value of art is that it can do this not only by stimulating our senses in satisfying ways that are already familiar to us, but more so than this, art can fundamentally change the very way in which we perceive reality. Now it should be clear that in many cases even the definition of what constitute aesthetic beauty is fluid and often learned, as a result aesthetics become inseparably linked with the perception altering aspect of art.
This is what made the Renaissance artists truly great, not just more realistic looking pictures, but the shift in perception that allowed the realism to be seen. The invention of perspective is probably the best example and is such a fundamental shift we take it for granted today that perceiving it is not an innate ability but learned. As an example, people from cultures lacking contact with the modern world do not see realism in photography the way we do, they see what is actually in front of them: a flat surface with colourful smudges.
Realism has been done, it is fairly well established in the realm of the familiar. Many artists have moved on seeking new ways to open up and challenge our perceptions. It shouldn't come as a surprise that without foundation or context, the viewer sees nothing more than some "colourful smudges" in modern art.
This ability to make new things visible to us, is what makes art arguably as important to advancing our society as engineering or some other more "respectable" vocation.
All of this is not to say the world of art doesn't have its share of pretenders or rich people more interested in using art as display tokens of their status, rather than an actual interest in its meaning. However, it's very easy to succumb to the allure of denouncing anything we don't understand as therefore having no value.