I just encountered this Reddit post which revealed the following answer to my question: see 12 herefrom.
##12. shrift
12. shrift
We might not know what a shrift is anymore, but we know we don't want to get a short one. "Shrift" was a word for a confession, something it seems we might want to keep short, or a penance imposed by a priest, something we would definitely want to keep short. But the phrase "short shrift" came from the practice of allowing a little time for the condemned to make a confession before being executed. So in that context, shorter was not better.