I read an article recently about a WWII-era tank discovered after someone dug quite far down into the earth, but what I can’t understand is where does all the earth come from the cover these artefacts? If anything I’d have thought that general erosion from wind and precipitation would expose items, not cover them.
While there's always more that can be said, you may be interested in some of these previous answers to similar questions:
This answer by u/kookingpot, about some of the processes that lead to burial.
This answer by u/AlotOfReading, about some of the conditions that make burial more likely, and why finds are more likely to be buried.