NPR featured a piece about seasonal eating and festivals in Germany. Check it out; it's well-written and on-point.
What I found to be especially true is the part about shoppers being accustomed to a smaller selection of produce featuring what's in season at the discount supermarkets. Indeed, this is the case at Aldi, Lidl, and Penny. When I'm cooking things that are out of season, I have to visit the big guys like Real or Globus.