The EDZ and Europe as a whole, actually scratch that; Terra as a whole has been contested by about 5 different forces. Humanity (including Warlords and Iron Lords and guardians), the Eliksni, Cabal, Hive And Taken. The Eliksni in lore have destroyed Old London. The EDZ is just their most recent loot plunder. Look at both versions of Widow’s Court. It’s ruined, and the rubble covers a lot of the places where overgrowth would take place. Cabal have made a massive base in the EDZ so that’s covered a lot of that. Hive have buried into the ground which would cause loose structuring of buildings. Taken don’t really seem to cause structural damage that we’ve seen with the exception of leaving blights everywhere. Humanity; well a battle between Warlords and Iron Lords in the Dark ages cause the town that Drifter lived in at the time to be destroyed. If you go to Mars or Venus or even Titan; a lot of the old architecture is still there, albeit in bad shape. The buildings that still stand all over have shown the affects of time; but due to factions/races contesting each other, they have seen structural damage which in turn ruins the plant’s ability to grow as we’d expect.