The terrain rises quickly beyond the departure end of RWY 03. The max allowable take off weight for RWY 03 even with headwind is less than RWY 21 towards the sea even with a tailwind. Thus, many A320 family flights choose to depart on RWY 21 to be able to uplift more PAX, all the fuel required etc.
Should RWY 21 not be available (too much tailwind), often Airbus flights need to stop at Sevilla/Frao/Jerez for more fuel to get to Germany, GB and beyond.