The sharper grip angle keeps the bore-line close to the center of your hand/arm, minimizing muzzle flip during firing. Mechanically, they are a simple, clean design, with 1/2 to 1/3 less parts than many comparable service-style pistols. They are darn near rustproof, easy to disassemble and reassemble, and have a very short trigger reset, making them easier to shoot accurately at high speed than many other designs. Finally, the design allows most owners to do all their own maintenance and upkeep, and even most customizing, if you are mechanically inclined at all.
"Placement is power" -- seen in an article by Stephen A. Camp
(RIP, Mr. Camp; you will be remembered, and missed)