Are you just relying on the Award Map? It doesn't show a lot of Spanish cities for me at all, you need to search for them. And I see plenty of availability in CE on Saturdays.
MAD Madrid has 2+ seats 10th, 17th and 31st
BCN Barcelona has 2+ seats 3rd, 17th and 31st
AGP Malaga has 2+ seats on 10th and 17th
ALC Alicante has 2+ seats on 10th, 17th
Which cities are you looking at in particular?
I wasn't looking at the award map, and was searching city by city, then using the calendar option to click on the days with availability. This is an add-on segment from a flight from the US, so we also have to consider connecting times. The availability I saw was for early morning flights (that we would miss entirely) or not on the Saturday we're looking for.