Let me direct you to a little known part of the US Government called the "NSA". They spy on citizens on the US and on citizens of other countries without a permit. (PRISM)
You see, the companies that operate with things like the NSA to spy on people have to store the voice data somewhere but it is heavily compressed yet the system sends to the recievers of the voice the compressed sound resulting in the quality that is often called "Worse than a telephone".
However, older games and programs like discord which dont work with agencies like the NSA dont have to store the data and just send it to the recievers and then deletes it leading to better voice quality.