The search for "why" is both very human and a big problem in terms of explanatory power. That is to say, someone has a finding and publishes it. That may (or may not!) be relevant to the specific tight scope around the survey/research. However, be very, very, very cautious in generalizing - that's where most people in ads/conversion optimization go wrong.
Back then, it took weeks to figure out which ad copy had better ROI. Now you can do huge tests and figure things out in minutes.
I don’t think there’s been any huge breakthroughs in a long time. All marketing/advertising is just recycled and presented in slightly different ways