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

They often turn up in rivers and canals in urban areas where they have been stuck in the muck.