The Boeing 747 was introduced in 1970, and we're still traveling at around Mach 0.85. In the past four decades, we haven't made any significant improvements to travel time.
The market largely seems to have decided that supersonic flights aren't worth the cost or the hassle; the push has been toward slightly smaller, more fuel-efficient twin-engine craft on the long-haul routes. Which pays technological dividends of a different, but less flashy sort. Hence publicity stunts like flying a 747 on one 777 engine (it works, and think what a 1970s-era person seeing a 747 for the first time would think about hearing that).
The market largely seems to have decided that supersonic flights aren't worth the cost or the hassle; the push has been toward slightly smaller, more fuel-efficient twin-engine craft on the long-haul routes. Which pays technological dividends of a different, but less flashy sort. Hence publicity stunts like flying a 747 on one 777 engine (it works, and think what a 1970s-era person seeing a 747 for the first time would think about hearing that).