[spectre256]

I'm not an expert, but I believe the reason comes down to cost: call center lines can be configured either to have a few high quality calls, or more lower quality calls (think of how many more audio files you could stream simultaneously at a lower bitrate). Of course, having lower quality calls lets them handle the same number of calls at the lowest cost, and most businesses consider customer service to be a huge cost center, so they go for the cheapest thing.