From local recycling company Phoenix Recycling:
"The problem nationwide is that there are very few large scale glass consumers and those are flooded by regional supply. Compounding that problem is the material they seek versus the material that is generated. Most recycling programs are 'single-stream' now, meaning that co-mingled material is collected and sorted at a MRF. The resulting glass is a grey 'sand' that is not color separated and generally not in demand for glass consumers."