I absolutely agree that better running, more reliable, longer lasting engines are a direct result of, for one, the technologies developed for emissions and mileage mandates. The evolution from carbs to multiport fuel injection is probably the biggest leap.
The evolution of computer technologies, "thinfilm" and resulting microchips, now used to control fuel metering and timing, is another huge contributing factor. And with that high-tech revolution came CAD/CAM software that even the science fiction writers could not have imagined. Nobody could have dreamed of the design power in these programs.
I'd add that there's an additional "driver": cost. The shift in manufacturing philosophies from focus on quantity shipped to focus on consistency and erroor-reduction drove concepts such as Design For Manufacture, Statistical Process Control, and Value Stream Analysis, all of which have dramatically improved quality and longevity, particularly in engines.
And, of course, there are wonders to behold in the materials area. Reverse gravity casting alone was a huge leap in the quality of castings.
Lots of good stuff converged over the last half of the 20th century to create engines that are truely amazing.