The dominant Yorba Linda housing era is the 1980s through the 1990s, with continued building since. That vintage does not have the galvanized problem and generally does not have the 1960s copper problem either — the systems are newer and the materials are better.
What it does have is scale. A 3,000 to 4,500 square foot house has substantially more plumbing than a 1,400 square foot tract home, more fixtures, longer runs, and frequently a second storey with bathrooms above living space. A supply line failure upstairs has a whole floor structure and a ceiling to move through.
It also has rooms nobody goes in daily. Guest wings, formal rooms, downstairs powder rooms in the far corner of a plan. We routinely find leaks in Yorba Linda that have been running for days simply because nobody had reason to walk into that part of the house.
The foothill terrain adds the second factor. Elevated properties on slopes have drainage that has to work, and slope drainage silts up quietly. Homes cut into hillsides can develop moisture at below-grade walls where the original waterproofing has aged out.
Equestrian and large-lot properties in Bryant Ranch and the eastern edge add long private water service runs, irrigation systems moving a lot of water, and occasional well and septic infrastructure — all of which fail out of sight of the house.