conversion is intrinsically lossy, but second, and more importantly, the digital signals used by the telcos were not "linear": they did not encode all frequencies the same way, instead utilizing a nonlinear encoding (u-law and a-law) meant to favor the nonlinear response of the human ear to voice signals. This made it very difficult to find a encoding that could survive the digitizing process.

Modem manufacturers discovered that, while the analog to digital