Planes in the ~80s were flying NY<>London faster than today -- the fuel savings generated by flying slower are what is driving the decision.
Not quite the first time: by looking at 1958, the start of the jet age, you have deliberately set as your starting-point the exact point at which they got things right, along that particular dimension (speed). Prop planes such as the DC-3 were most certainly slower.
But it's true that commercial airliners have not got much faster over the past 50 years, and that's, as other replies to your comment point out, down to the speed of sound.
For instance take a look at liquid-fueled rockets. The first one was built by Goddard in the 1930's, they advanced rapidly with the German V-2 and then the Soviet and American military and space programs, reaching a peak with the Saturn V that has not been exceeded to this day.
Going supersonic uses 3x the fuel. That's what killed the Concorde.
The 757 use to make the SFO-JFK route in a little under 5 hours, these days most flights make it in just under 6 (a 20% increase in time to save fuel).
Air travel is technically capable of big improvements, but economics don't work out.
There's a sweet spot where fuel savings, customer satisfaction, and capital costs meet, and it's at a much lower speed than engineers are capable of producing.