Copyright law was insufficiently specific about copied media, which I guess wasn't much of an issue when pressing discs way back the, and in retrospect it's clear the Congress hadn't been captured by the RIAA, heck, I suspect back then they weren't too popular, so it took quite some time to close.

This was big enough to be covered in US News and World Report, the general weekly news magazine my parents subscribed to back then (competitor with Time and Newsweek). Time period would be in the early to mid-'70, or at least that's when my family started doing this for a few years.