Well, the article linked to implies that the reason for the flat aspect of the artwork was that they were more interested in strongly conveying themes and conce

Well, the article linked to implies that the reason for the flat aspect of the artwork was that they were more interested in strongly conveying themes and concepts than they were reproducing what the eye sees. The article compares it to a modern comic strip. Whether they "couldn't" draw perspective, or were just uninterested, I don't know. I believe it was the Greeks in the 6th(?) century BC who were the first to use linear perspective in their art.