[handyman5]

You are not controlling for the programmer's age as a variable. An equally valid explanation could be that newer programmers have less experience to draw from, where older programmers have more experience and know what works and what doesn't. Or, alternatively, newer programmers might just be a much larger pool of people, and perhaps more people stop programming as they get older than start, so that the average skill of an older programmer is much higher than you might otherwise expect (since all the low-skill programmers quit when they were younger).

[hedora]

This. My day-to-day code has probably doubled in efficiency every 2-4 years since the mid 90's.

Granted, a decade of that was chasing hardware trends, but the earlier optimizations stack too.