Customers asked "why aren't there any review saying a product is bad", so they started doing that with products whose manufacturers didn't advertise there or didn't give free stuff for review. They'd borrow, or buy a few Danelectro or Behringer pedals for $30 dollars just to make a bad review and "save face" to readers.
Basically they got "token bad products" to save face.
A decade plus ago I worked alongside a team of writers, and they always kept alcohol in their desks. I totally understand why now.
You definitely need a bottle for when you get some terrible product and you know the manufacturer won't like that it won't get reviewed.
Funny enough, the situation is even worse now: with YouTube reviewers, there's no more expectation of neutrality as with professional journalists in the past. So all quality reviews are praising products.
They got a guitar or synth that was bad? They would just tell the manufacturer they would rather not say something bad.
Of course, after a while readers started asking questions, so the answer was to review products from companies not advertising in the magazines.