I understand completely. Several years ago I donated several baby quilts, 8 zippered baby sleepers (with cute appliques), and a quilted baby bunting. I enclosed a note that said I could make the sleepers in different sizes, if they would let me know what sizes were most needed. When I didn't hear anything back, I wrote a letter asking if the packages had been received, and enclosed a self-addressed stamped envelope. Still didn't get a response.
I wasn't looking for an outpouring of gratitude, but if they had simply written thanks, we received the boxes, I would still be sewing for them. As it was, I found another charity. It's just human nature to need some acknowledgment.