I try to feed a variety of products to the wild birds.
The only type of seed that they throw out is the "whole" sunflower seed, ie the ones with the black husk. These get chucked out of the feeder by the small birds, and the pigeons eat them off the ground.
But the white sunflower hearts are very popular in the mix of seeds in the feeders and are always eaten by the small birds (a variety of finches, sparrows, starlings).
If you are feeding only sunflower hearts, and your wild birds are throwing them on the ground all the time, whether they are the cheap variety or the more expensive ones, I think I would come to the conclusion that they may be tired of sunflower hearts. At this time of year they can afford to be picky as there is an abundance of naturally occurring food available.
Try feeding a mixed variety of seed and then introduce the sunflower hearts again when the weather gets colder.