In my estimation, the Ruger is the Ford Truck of handguns. They're totally reliable, do what you bought them to do without fail, and they do it pretty well. That said, they don't have all the frills, bells, & whistles of some other guns, and they aren't necessarily the best handguns out there in any or all categories.
It's sort of like saying, "Why is a Ford F-150 cheaper than a Ferrari?" They're different kinds of automobiles. The latter is probably much more fun to drive, goes faster, handles better, and looks nicer. But if a man could only afford one automobile for the rest of his life and had to choose between the two, I could easily see why one might choose the Ford. More durable, wider range of uses, less finnicky, solid, & proven. I'd rather have a $250 Ruger P95 as my truck/boat/stashed wherever gun than a $700 H&K P2000. If I have enough to buy multiple guns and/or replace my P2000 if something goes wrong with it, then it doesn't matter much. But I could take that $700 and almost buy 3 P95s to arm my whole family with that will last forever.
Their reputation for reliability and toughness precedes them, and in my experience that reputation is well earned. Bang for buck, they're tough to beat. Why are they less expensive? Well probably in part because they're less expensive to make (blockier ergonomics, less economy of size/weight, etc.), and probably in part b/c Mr. Ruger's goal was to have a reliable, affordable handgun that an average working man could afford with one paycheck. A Sig, H&K, or custom 1911 they are not, but they have their well earned place in the firearms world for a reason.
