As someone who has been a foster for several years, I'd suggest asking them (there is an excellent Foster Survey available through Maddie's Fund).
Some possible reasons for a lack of response to fostering might be:
(1) the holiday season and not wanting to take on another responsibility until it's over;
(2) misperceptions about the breed and its needs (some look at all dogs of a certain breed as being the same instead of individuals);
(3) fostering for other rescues and the foster cannot take another dog;
(4) age and general factors of the foster's resident dog (my 12 yr old Golden does not tolerate young, exuberant dogs).
Hope this helps!
------------------------------
Elizabeth Smiley
Desert Labrador Retriever Rescue
------------------------------