Boeing B757 is an aircraft developed in 1980's to replace fuel inefficient, noisy B727 trijet, and is the largest single aisle in the world.

Because of this, both Pratt Whitney & Rolls Royce have to develop engines of 35000-43000lb thrust, PW2000 & RB211-535 respectively for the aircraft.

B757 has excellent take off performance, thus very suitable for airports with short runways or hot, high altitude conditions. This and its long range (8000km for -200 & 6800km for -300) and its 3 hours ETOPS capability makes it a very versatile aircraft. So it is widely accepted in USA, as well as less developed places China, Africa, and Iceland, which has harsh climate & air traffic insufficient to support widebody operations. It is also widely accepted by many charter airlines.

But its narrowbody design makes its sales poor in Asia except China, because most Asians prefer taking more comfortable widebodies of similar capacity as B757 like B767, A310 & A300.

If B757 is improved further so it has 10000km range, then there would be more non-stop air service not sufficient to support widebody operation, thus making B757 more popular.

How good it will be if Airbus produces A322 & A323 competiting B757-200 & -300 with more range & more commonality, so airlines can operate more point to point routes not sufficient to support widebody operation, while they can reduce flight crew training & maintenance cost compared to B757.