How are WW1 or WW2 era bombs still regularly found in gardens and houses around UK and Europe?

Question

The day after or week after these were dropped 60-100 years ago, did people not think, there’s a bomb over there we should make it safe.

Edit: I singled out the UK because they discovered a bomb from World War Two today in Plymouth. I know the UK is still in Europe.

In: Other

Answer 1

WWI consumed about 1 billion (with a **B**) artillery shells. Even if the failure rate (shells that do not detonate) was as low as one in a thousand, that means there would be one million “dud” artillery shells laying around in Europe waiting to be found.

WWII had all that and more.