Because nearly every service auto from 1911 until the '70s has become obsolete. Those designed since then, Glock et al, are made to be cheap to build, light to carry, simple to operate, and durable in the field. That gets them government contracts.
The 1911 is made to shoot. Getting a good 19th/early 20th century design made right in the 21st runs the cost up, but I think it is worth it.
It shoots. By that I mean that it just feels right to me and I do not have to work as hard to shoot accurately as I do my P7 or my G23 (notice I did not say Glock) because of the trigger pull and slimness of the grip. I love it when I can introduce the 1911 to the modern DA/SA shooter at the range. They often say they had no idea they shot that well.
My hunting buddy is a confirmed Beretta pistol owner, and has a M84 in 380 and a Cougar in shorty forty. I have handed him one of my 3 series 80's on several occasions, and he obviously shoots them better than his own pistols, yet will not entertain the idea of buying a Colt, even though he hits better with them and complete teardown is not the nightmare his are. Go figure............
The 1911 is the best purely-designed fighting handgun ever made. The combination of large caliber, short trigger reset, and ergonomic design makes it tops. The new designs only better it in ease of manufacture and carry weight.
As stated before, the 1911 is the best combination of power, size, ease of handling, and user friendliness. All rapped up in a package that is not only inherently reliable but also a technological marvel and joy to look at.
Why are 1911's the best? Here's a few good reasons:
1) Best trigger in an auto period
2) Most are asthetically pleasing to the eye
3) Can be had in numerous calibers (although I prefer a 45)
4) Combat Proven in 2 World Wars and numerous conflicts.
5) Parts are readily available
6) Easily customized
7) Fits most hands well
8) Numerous manufacturers to choose from
9) Can be made extremely accurate
10) The design has no equal even after 90 years.
Hey, just the mere name "1911" means something. It means "since 1911", much like aged wine that has finally matured. It means constant refinement over 90 years of use. It means old-world quality and durability. It means forged steel. And its name was given by the world's most powerful military, not by a bunch of execs sitting around a table.
Besides, how could you possibly call #1 a gun who's name sounds more like a strangled chicken?