Two things line up in this area and neither one is dramatic on its own. First, the age of the housing: most homes were built between 1962 and 2005, with the bulk of that stock - across the roughly 44 named areas that make up this part of the county, from close-in neighborhoods to places out toward Maple Valley and Black Diamond - dating to the 1980s and 90s. That's a lot of garage doors hitting the same failure window at roughly the same time, because they were installed in the same building boom.
Second, the climate. This is a mild band with occasional freeze, not a place that destroys doors with heat or ice storms. But that occasional freeze matters more than it looks like it should, because a steel door with no insulation and no thermal break will sweat and frost on the handful of cold mornings each winter, and that moisture is what rusts hinges and swells wood trim over time.
With 213,261 households and 118,318 owner-occupied houses across the service area, and a median household income of $131,283, replacing an aging door with a properly insulated one is well within reach for most owners here - it's just that a lot of people are waiting for the failure rather than getting ahead of it.