I wish I could say it started with Walmart and their drive to push down costs from suppliers. But I now believe that they just took advantage of a situation that was already in the making. The drive to cut corners in every aspect of manufacturing in the name of profits has made every possible thing disposable.
I just inherited an early '70s stereo receiver from my dad. When I opened it up, I was shocked to see the cover was walnut and not plastic. It just goes to show that as product quality degrades, our expectations degrade along with it.