May I ask why the downvote? My speculation may or may not be correct, but despite @brandonmenc's objection, I still think it's a possible factor. It certainly

May I ask why the downvote? My speculation may or may not be correct, but despite @brandonmenc's objection, I still think it's a possible factor. It certainly matches the attitudes of my relatives and other adults when I was a child growing up in the 80's. It's also more closely tied to the start of the trend line than some of the other theories in this thread, and was posted as a good faith response to @cguess.