The answer to a question nobody asked for? Oh, really?
Posted before:
Why the .40S&W?
It has been essentially called for for some time, and for good reason.
1870s - Catridges looking a lot like the .40 S&W and 10mm began to be worked on. The .38/40, as an example, pushed a 180 grain bullet at approx 950 feet per second. Not bad for black powder.
1960s - Folks started looking for what they considered "the ideal" revolver cartridge, a .40 cartridge which could push 200 grain bullets between 900 and 1000 feet per second. Folks like Jordan, Keith, and Skelton, mind you. (They didn't get it, instead getting the more powerful .41 Magnum; a great cartridge relegated mostly to field use having been deemed too powerful by most for every day carry and defensive use.)
1970s - Col. Jeff Cooper, Mr. .45acp, called for "the ideal" semi automatic cartridge, one delivering a .40 caliber 200 grain bullet at 1000 feet per second. The 10mm began to take hold. (He didn't get it, instead getting a more powerful 10mm; a great cartridge... deja vu... deemed too powerful by most for every day carry and defensive use.)
The 10mm began to be loaded in two varieties; the magnum variety which has proven popular with 10mm advocates, and the variety often referred to as the "down loaded" and "light" 10mm. (The weaker cartridges look an awful lot like what the greats had called for, but what did they know?)
1980s - the FBI adopted the 10mm in the form of a 180 grain JHP at approx 950 feet per second. There never was a stronger one or a weaker one. That was it, and the agents apparently liked it. (The whole "they went to the .40 S&W because agents couldn't handle the 10mm is incorrect: the .40 S&W they shoot today is marginally more powerful than the 10mm load that they moved away from.)
Meanwhile, other folks had been experimenting with cartridges capable of duplicating the FBI spec'd 10mm's ideal; a nearly hundred year ideal. And someone asked: can it be done in a more size-efficient package than the 10mm? The answer was yes and in 1989 the a .40 S&W load was introduced pushing a 180 grain bullet just shy of 1000 fps.
The .40S&W currently dominates the US law enforcement market and is very popular in gaming circles.
Why?
LEO wise: Many law enforcement agencies took note of the FBI's declaration that a 10mm 180 grain JHP at approx 950 was "best" for LEO/SD purposes. And some of those folks were gunnies who remembered what the greats had called for all along.... They also took note that the .40 S&W fit into 9mm sized frames, and liked the capacity offered by a round beginning with "4." Good performance, smaller pistols, and increased capacity? Winning combinations.
Gamer wise: 180 grain bullets at 1000 feet per second make major. Making major while affording more capacity? A winning combination.
Non-LEO/SD wise: These folks, many of them at least, pay a lot of attention to the afore mentioned folks; greats, LEOs, and gamers. They began to see more and more pistols chambered for .40 S&W, and that's all that it took.
Now a days, there are a variety of choices, with the 155, 165, and 180 grain varieties being the most popular. Gaming and bipedal fighting wise, you could do worse. The two main federal labs (DOJ's and DHS's) currently spec the 180 at approximately 1000 fps as "ideal." (Just over from most duty pistols, iirc.)
Note: Not your cup of tea? Fine. But the the .40 S&W doesn't deserve half of the flak people like to send its way.
And it certainly seems that along the way folks asked for it; if not it, something similar enough to allow for it to fit the bill.