Airlines used to post their flight schedules on brochures with the ticket cost. While I was researching this topic, I found that the American Airlines flight from New York and LA in the 1960's was 5 hours and 43 minutes. This flight was planned to take off at noon and arrive at LA at 2:43 pm with layover. Nowadays, the flight still is scheduled to leave at noon, but is is scheduled to arrive in LA at 3:27. Way later that in the 1960's.
This has happened on every airline. Almost every flight takes longer today than the 1960's. This mostly because there is more security checks. And generally, it just took longer to get to the plane.
All the time the plane spends in the air is the same. But the delays and all that just slow down the process of the flight.
Nowadays, the delays account for the time it takes to get there.
Engines There are three types of aircraft engines.
The Turboprop, the Turbofan, and the turbojet. Each one has a range of speeds where they are the most efficient.
The turboprop is the cheapest one of them all. They are generally slower than the other two though. This is why you see them being used by small commercial airlines. Their range is from 300 mph to 400 mph.
The turbofan is what you usually see when you go on a commercial airplane. The turbofan engine has a fan in the front that speeds up the air. Then most of the air goes into the internal combustion chamber which speeds up the air even faster. They have an effective range of 500 mph to 600 mph.
The turbo jet is the normal kind of jets you see on jets.
The Planes The last commercial plane that used the turbo jet was the Concord.
It seats only one hundred passengers. Compared to the 787 from Boeing, the 787 holds almost 200 more passengers.
The Concord is also not efficient. The 787 has a 104 mpg while the Concord has a 14 mpg.
It also takes $7,500 to have a one way trip from New York to London.
The reason put simply is that flying faster is just way more expensive.