Pulaski

That is the "modern engine" factor. New cars (say, last 20 years) are made to much higher engineering standards and the engines shed less "gunk" as they bed-in, and wear.

Also full synthetic oil is a significantly better lubricant - anecdotally it is worth 5% on your fuel economy, and so there is less grinding of metal on metal, and therefore less debris in the oil.

I remember my father changing the oil in his car when I was a kid, per the service intervals, and what he drained out was filthy black oil. The oil in my cars' engines over the past six years that I have been using full sythetic oil is still a good clear color even when a service is due, it only has a slight mistiness of dirt in it. .... Maybe oil filters are also better than they used to be?