Copy protection of tape games took a different form. It wasn’t that you couldn’t make a copy, but there were extra barriers to making it playable. Eg Jet Set Willy came with a card on which was printed a coloured grid, and upon loading the game prompted you to enter the colours found at random coordinates before it would start. http://www.computinghistory.org.uk/det/57256/Jet-Set-Willy-C...

Copying that card was high effort, since no one had camera phones or scanners or photocopiers etc.

I seem to remember some tapes were designed to load faster or otherwise decrease the margin of error when reading the tones, such that it wouldn't easily survive the degradation of tape to tape copying. Probably at the expense of the original not being as reliable.

I was a kid at the time so could be wrong about this.