2d Depth of field

Why does the sprite not have near and far depth of field blur, only 3d objects have it. If the sprite is in front of the 3d object, adjust the 3d object and the sprite has depth of field, for example:

 

Depth Of Field calculates its results based on a depth buffer. Sprites and other objects with alpha-blended shaders usually don't write depth. Figure out how to write depth from your sprite and you'll be good to go.