It’s because reality is complicated. Most people don’t want “dark mode” as a pure accessibility feature in the sense of “whatever color scheme is fine as long

It’s because reality is complicated. Most people don’t want “dark mode” as a pure accessibility feature in the sense of “whatever color scheme is fine as long as it’s dark everywhere”. That’s the reverse color feature in most OS. Instead I/they want dark themes but with pleasing colors, adjusted depending on the screens and the widgets, having sane defaults for content that is usually supposed to be white, with exceptions. Yes, that’s a tall order, it’s context dependent, and we might actually want to decide app by app if the dev did a good job and/or if dark mode makes sense, and sometimes change the theme in the app because it’s otherwise not great. We end up in a patchwork of apps following dark mode and others not, with different themes applied that might not be triggered by the system. For instance I use youtube, reddit and editing apps in dark mode only, while the rest of the system is in light mode. As you say it could be handled by the system in a super granular way, but it would add that much more complexity, and I actually chose the exact themes to be used in most of these apps, so centralization wouldn’t help anyway.