Why Do AI-generated Portraits Fail at Realism?

This is the promise made by AI Gahaku, one of the most popular artificial intelligence engines trained to generate images that resemble old paintings using our own pictures. It is simple as it sounds: You upload a photo of a face, choose the painting style, and voilà, the AI generates an image that looks like a century-old Western portrait ready to be displayed in a museum. The success of AI Gahaku follows the success of many other apps and projects that over the past few years have experimented with user pictures and AI filters. AI Gahaku claims that "various painting styles can be easily applied to it such as Renaissance, Pop Art, Expressionism and many more!" It would be too easy to deem the popularity of AI-generated portraits resembling old paintings as due to the nostalgic enjoyment of figurative art styles that are safer and easier to understand than modern art.