Because having medieval housing in the galactic era would be weird. I can just push it back to another tech after civil engineering.
Idea for a new national wonder:
Emergency Grain reserve (might want a different name to differentiate rom strategic grain reserve, but that's a detail): Increase food required to grow in all cities by 5% BUT provides up to 4 food/turn to any city that is in starvation. I think the Python to do that would be quite easy (would run on doTurn() and would not be expensive to process)