It doesn't, but heft of a product is used as a proxy for quality, to the point that electronics will sometimes have a weight glued inside to pretend the item is heavier than it is, in order to seem of higher quality.
Which greatly illustrates the point that it's mote of a feeling than inherent property. People got used to expect crap quality from lighter products, because at the same time as plastics became more available and more versatile, so did planned obsolescence. So they are fallaciously expecting a heavy item to not having been cheaped out on so much.
It doesn't, but heft of a product is used as a proxy for quality, to the point that electronics will sometimes have a weight glued inside to pretend the item is heavier than it is, in order to seem of higher quality.