I'm sure that someone with more expertise will chime in, but most tape outputs are not controlled by the volume control - it would make taping a bit inconvenient if you had to leave the volume know untouched during taping! In fact, if I understand it correctly, most are just a direct connection from the source (or phono preamp), since the line stage is usually after the volume control. Some suggest buffering the tape output - I don't know the necessity of that in practice.
HTH,
Pete