Every field that I know that has been lost was due to encroachment of population. They start off in the boondocks and as houses, etc. move closer eventually they are lost.

Two things:

1 - the general public does not want to listen to toy airplanes buzzing around

2 - the general public does not want toy airplane buzzing around over their heads/homes/land

A very small number of fields are lost due to changed land use, i.e. the farmer decides to plant the land, etc.