> Chrome is in maintenance.

Unfortunately this is not good example, because Chrome undergoes continuous refactoring and is always adding new web features. Even V8, which I worked on for almost 7 years, is definitely not in "maintanence", as JS changed radically in that time and we added the Wasm engine subcomponents.

I kind of agree with your other points, but this is really a spectrum. For example, a 115 year old house is in "maintenance mode", yet it needs new insulation, wiring, upgrading the heating/cooling, interior redesign, floors, windows, etc.

The truth is that most long-living systems are composed of many different subsystems which run the spectrum from "install once, fix it when it breaks" to constantly being rejiggered.