So, the question of ability and quality in various art historical periods is a complex one, and the terms you have set in your question reveal somewhat of a presentist bias. One might rephrase the question as "Why does the art of medieval France/eleventh century China/ancient Greece not look the way that European art of the late 14th to the late 19th centuries look, as I understand this art to be the most 'realistic' ever produced?" In other words, it presupposes that the art of the Western academic tradition best approximates a fixed and immutable "reality" that other cultures have tried but failed to approximate.

This is a common perception. It is also, according to essentially the entire field of art history, erroneous. Below I will try to elaborate why, and point you towards some sources for further reading on this subject:

First of all, when you refer to art as "realistic" and "detailed," you are referring to the tradition and style of artistic "naturalism." We art historians contrast naturalism with realism because there is a specific historical art movement, mostly based in France in the middle of the nineteenth century, that has taken the term Realist, and so it's better to call "realistic" art naturalism instead. The Realists, the most famous example of whom is probably Gustave Courbet, worked in a naturalistic style, but their movement went beyond an attempt to replicate the world around them and into a social and political dimension. The Realists were concerned with representing common people and everyday life, something that previous generations of artists had avoided in favor of representing the elites of society. This turn towards the everyday often had a specifically leftist political dimension, as these artists lived in a time and place (Second Empire France) of considerable political repression but liberalizing social mores. A famous example of this style is Courbet's The Stone Breakers, which unfortunately was destroyed in a WW2 bombing raid.

Since the beginning of the Renaissance, European artists and artistic thinkers have privileged the representation of people, animals, and the built and natural worlds as they actually appear. Since the artists who came directly before them, during that long period of time we refer to as "Medieval," tended to paint in a stylized way, this has led to an assumption that the painters of the Renaissance were more "advanced" than their forerunners. This is an assumption that the painters of the Renaissance would have been all too happy to encourage, tireless self-promoters though they were. In fact, just as historians more broadly have rejected the Whig History view of historical time, in which history inevitably moves along a straight, progressive line towards a "more civilized" present and future (which always seem to be represented by the dominant strain of White European thought and culture), art historians have rejected an idea of art moving from a simpler, more "primitive" mode of representation to a more sophisticated and naturalistic one. As other posters have pointed out, during certain periods Roman art features a striking naturalism, and Greek and Roman sculptors also show a great ability for naturalistic representation. Yet, though many of these sculptures may look like real people, they are often not particularly close representations of the actual people they purport to represent, but rather idealized types. You can also find striking examples of naturalism as far back as the Chauvet caves, the earliest known surviving paintings, dating from at least 30,000 years ago.

So, why did people of other times and places choose to paint the way they did? And why did naturalism win out in the European imagination post-1400 (or so)? These are tricky questions. The general answer to the first (and thus, in a way, to the second), is that artistic style reflects the wider cultural, economic, and social forces that affected the people making the art. So, to take as an example the art of the Byzantine Empire ca. the 11th century (and please, medievalists, don't come down on me too hard for errors, though I welcome clarificaiton): This was a culture that highly valued a mystical connection with God and the Saints. The experience of art was tied to a ritualized religious context in which music, incense, and other inputs helped to conjure the "real" presence of the individual represented in an icon. These were not representations of, say, the Virgin Mary, but her actual embodied form. It's similar to how for Catholics the host and the wine literally become the body and blood of Jesus.

So why naturalism for us modern Westerners? Well, since the Early Modern period we have lived in a time of ascendant capitalism, when the ability to determine truth from fiction, to explain, categorize, and dominate the world around is, us paramount. We have developed a preference for art that reaffirms our desire to control and possess the world. By representing things, we can seek to increase our mastery over them. There are also technological reasons, including that oil paint (which wasn't widely introduced until the High Renaissance) better represents human flesh than tempura (egg-based) paints, and the development of photography, which has primed us to expect a great deal of naturalism in our representations.

Sources:

Pentcheva, Bissera. Space, Ritual and the Senses in Byzantium

Errington, Shelly. The Death of Authentic Primtive Art and other Tales of Progress

For a look at the limits and limitations of looking at pictures historically, I like Michael Baxandall's Patterns of Intention

This bibliography is somewhat less complete than I'd like, but I'm going to press "save." I'll update it later when I get a chance.

Hi, not discouraging a more direct answer here, but FYI, there are several posts on art in the FAQ. The section is organised roughly chronologically.

• FAQ section Why wasn't ancient art realistic?

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