Conversely, that's what's amazing about the Web, right?
Whenever people introduce any of those things, like when iOS was introduced, they had to decide how to port all the existing content and interactions and widgets to mobile and touch interfaces. As a result, if an entrepreneur or hobbyist makes an app on one platform and wants it to be at least minimally usable on another platform, the Web way, way lowers the barrier to make that jump.
The particular methods for making CSS backwards compatible are specific to the web, but the general problems faced by having user display preferences are not. Adding these features to native apps blows up your testing matrix there, too.
In many ways, it's even worse. I've got OS settings here for "increase contrast", "reduce transparency", "use grayscale", "invert colors", and (because areas of native windows can be translucent) even the desktop wallpaper comes into play.
I turned on dark-mode for testing my own app, and I had to turn it off because there's parts of Xcode where the contrast ratio is less than 1.1:1.0. The text is downright invisible. Obviously nobody at Apple would ever intentionally make software like that. They must have simply never thought to test with the same settings as I have.
And yet Xcode is very successful and well-liked, or at least if it's hated, it's not for the flaw you found.
Doubtless many, many other apps have also made that same mistake, yet I highly doubt it has made the difference between success and failure for even a single one of them.
All of those OS features were introduced to help people, because people wanted them, some even needed them. I don't think we live in a worse world for having them, and I believe that dealing with features like those would actually be even harder in a world without the Web.
Whenever people introduce any of those things, like when iOS was introduced, they had to decide how to port all the existing content and interactions and widgets to mobile and touch interfaces. As a result, if an entrepreneur or hobbyist makes an app on one platform and wants it to be at least minimally usable on another platform, the Web way, way lowers the barrier to make that jump.