I think the cost factor is the biggest reason. Previously you needed to dedicate actual people to listening in on conversations. You had a listening office with

I think the cost factor is the biggest reason. Previously you needed to dedicate actual people to listening in on conversations. You had a listening office with physical copper lines coming in and if you wanted to listen to a new line, you'd have to patch it in, which after a certain point means disconnecting a line you have less need for, because the patch panel only has so many connection points. A secure, end-to-end encrypted system would surely do a lot to increase the cost. But a big problem is that it's still very tempting to just poison the well and weaken the crypto/plant backdoors in the build infrastructure/whatever because that kind of thing enables bulk collection again.