FCFL (Fly Confirmed For Less) Fare higher than retail on delta.com

I’ve started planning our 2022 TATL travel.

Due to the rollover of miles and Medallion status I have many Global Upgrade Certificates which will expire if unused by 12/31/22. For those who aren’t familiar with them, the Certificates provide an upgrade from Main Cabin to D1. I was looking at airfares for travel periods when it would be nice to have ticketed D1 instead of relying on our parental nonrev priority.

I priced a retail trip on Delta.com, JFK-LIS-JFK for 5/10/22 – 5/19/22 and asked out son to price it as FCFL. The Main Cabin, Comfort+, and Premium Select FCFL fares were lower than retail BUT the D1 fare was higher. While I have no interest in purchasing D1, my reaction was ‘REALLY DELTA’, what gives?