Which attribute of the characters in morality plays reflects the fact that these plays were naive allegories?

They personified abstract concepts.

Explanation:

In morality plays, the characters that were present in the stories personified abstract concepts. Therefore, the characters were very simplistic as they only needed to successfully convey a single characteristic (beauty, courage, etc.). The resulting text would consist of a naive allegory, as it lacked the complexity that is characteristic of more realistic genres.