Most of the housing across this service area was built between 1961 and 2010, with the median sitting around 1981, and the bulk of it is 1980s and 90s construction spread across the named neighborhoods here. That's a specific window - it means a huge number of doors are running original torsion hardware that's now thirty-plus years into a spring rated for a fraction of that many cycles.
The climate here is mild temperate, not coastal damp and not desert-dry with wide swings like you'd see further out toward Byron or Discovery Bay. That mild band is actually part of why these springs last as long as they do before failing outright - there's less rust working on the coils than you'd get near the water, and less thermal expansion and contraction than you'd get out past Mountain House. But mild doesn't mean nothing: three decades of daily cycling wears a spring down on its own, climate or not, and 1981 was a long time ago.