Suppose an authors intent is to teach a moral lesson what best explains why the author might choose the genre of allegory to convey the lesson?

Normally the lessons of an allegory are straightforward and not too difficult to interpret. The lesson is easily learned.

Photography has changed its subject matter quite a lot over the past few years. in the 1800's, it was considered normal for families to have  post mortem photos of their loved ones, and now that would be completely unacceptable. i think that photographers have always pushed boundaries and have been eager to capture everything, it is just society that changes their boundaries.