POTTS lines aren’t secure either. Anyone between your house and the telephone switching equipment (miles from the location) can make a call that really appears to originate at your house, no spoofing involved.
And you are correct, there is very little security on those lines. In the 3/4 of a mile from here to the CO, I can think of 3 places where that could happen (without climbing poles) if I actually had a landline.
/johnny