Answer:
Painting needed to serve as useful and accurate historical documents, and therefore had to appear realistic.
Explanation:
There may be many reasons for realism in art before photography. One of them is that at that time, probably, artists and society weren't ready for other kinds of artistic exploration. If you think about it, artistic vanguards all came during the 20th century, when the world and humanity were in a different time and context. But before that, and before photography, art wasn't merely focused on the artist's expression and individuality. Artists served royalty and religion, and had the objective of working as a documentation of those times. Michelangelo, for instance, worked for the Medici family. And that's only one example. Kings of all countries had artists painting them, portraying life in castles, parties, births, etc. When photography came along, arts changed completely as it wasn't necessary to use it as a documentation tool.
