There's no excuse why a major metropolitan area of 2.5 million people can't support a full-size symphony of musicians who are paid a full-time living wage, especially when there aren't any competing organizations in the area. Albuquerque pays better, Omaha pays better, Tulsa pays better...and these are smaller poorer communities. Even The Las Colinas Symphony in Irving can pay its musicians better than the San Antonio Symphony.
Nearly every major metro area with over 1 million people in the US has a premier orchestra (full-time or not) where the average employed musician makes at least $35k/yr. The San Antonio musicians were offered half that, so they walked. Plain and simple.