Okay, that's a bit of a click-baity title. It's not so much about Dolby Noise Reduction being a scam (it does has its problems, though it was invented to mask worse playback problems), but tape equipment builders that use Dolby NR to hide their lousy pre-amp circuits.
Those of us who've had the privelege to use some high-end tape equipment may have noticed that switching Dolby on and off didn't really make a huge difference to noise reduction. Sure, we could pick changes, but they weren't outstanding. Changing tape speeds could show a much more noticeable change to sound quality.
But many would have heard it make a big difference on a lot of mediocre equipment, which suddenly become a hell of a lot quieter with it switched on. And if you did some experimenting, you soon discovered most of the noise it was reducing was not from the tape, itself:
If you had a machine that you could take the tape out and still run it in play mode (e.g. cassette decks), or lift the tape away from the heads (e.g. reel-to-reel decks), or play non-magnetic leader tape ahead of the recording tape, or a machine where using pause didn't switch in any muting-circuits (this could be on any kind of tape deck), you could hear that there was only a mild “shhing” noise when the tape was moving past the heads versus when it wasn't. But what was really noticeable that many playback pre-amplifiers made a lot of hiss (and other noises) all by themselves, which was much louder than the tape hiss.
Some deck's playback amplifiers had quite loud rushing noises, some have hum that's from poor power supply filtering, or the power transformer is getting into the magnetic pick-up heads. And rather than design their equipment better, they cheated and used a Dolby noise reduction chip to mask the noise.