Here's why:
* Mystery plays focused on biblical stories: The majority of mystery plays were based on stories from the Bible, particularly the Old and New Testaments. These stories featured concrete characters like Adam and Eve, Noah, Jesus, and the Apostles.
* Emphasis on the "mysteries" of faith: The term "mystery" in "mystery play" doesn't refer to abstract concepts, but rather to the "mysteries" of the Christian faith. These mysteries, while theological in nature, are often expressed through concrete events and characters in biblical narratives.
* Some allegorical elements: While the core of mystery plays was biblical storytelling, they often incorporated allegorical elements. These elements could sometimes touch upon abstract concepts like sin, redemption, and divine justice.
Therefore, while mystery plays did use some abstract concepts, their primary focus was on concrete biblical stories and characters.