A house built in 1976 has had roughly fifty years for steel to fatigue, wood jambs to shift, and the original spring - if it's still the original - to sit well past its rated cycle count. With only 599 households in Rainbow, this isn't a neighborhood that's been through a wave of remodels; a lot of these doors have had one owner and one door their whole life.
The mild temperate climate here has actually been kind to the metal - no hard freeze-thaw, no coastal salt air eating at hardware - so failure here tends to be mechanical wear rather than weather damage. Springs go from cycle fatigue, not rust. Tracks bend from decades of use, not from ice. That's a different failure pattern than we see in areas with harsher swings, and it means the door itself often outlasts its hardware by a long margin.