An architectural salvage yard looks like a cross-section of the past, everything the old houses held, laid out in rows. It isn't. It's a sorted remnant, and the sorting doesn't show unless you go looking.
Everything in the yard is there because someone, at some point, decided it was worth pulling free instead of crushing. That decision got made thousands of times, by wreckers and contractors and homeowners, each weighing effort against likely value in a few seconds. Parts that came out easily, or were obviously worth money, or blocked a careful demolition, survived. Parts that were fragile, buried, cheap-looking, or hard to reach did not.
Survivorship shapes the record
Survivorship bends the record. Solid brass and cast iron last because they're tough and clearly valuable. Delicate painted finishes and early plastics mostly don't, so the past looks sturdier in a yard than it ever was in the house. Whole kinds of parts barely appear, because they broke, or because nobody in a hurry judged them worth the trouble.
That's what makes a sound old piece worth noticing. It cleared a run of decisions that most of its contemporaries failed. A fixture in good condition is old, yes, and also lucky: judged worth saving, more than once, by people who had every reason to smash it and move on.
So the yard favors what lasted through hands and tools. It tells you a lot about brass, iron, thick glass, and parts someone bothered to carry out, and much less about what was fragile, cheap, or in the way.