Technological progress mostly relies on discoveries made in physics. Things that will amaze a 1885 person in 1950 were mostly made possible with electricity and derivative technologies, plus nuclear physics, and a few other things. Even engines for our flying machines wouldn't have been possible without electricity.

So the reason the leap between 1950 and today is not as noticeable in terms of the author's time machine experiment, may be because there have been no more major, truly groundbreaking discoveries made in physics, as in, e.g. discovering a new force in nature not known before etc.

But the author is of course right in saying that the past 65 years were marked with a lot of hard work rather than earth shattering discoveries.