You've not used e.g. Google Maps and have it switch to dark mode when you're driving at night or through a tunnel? But regardless of whether this can be useful

You've not used e.g. Google Maps and have it switch to dark mode when you're driving at night or through a tunnel? But regardless of whether this can be useful or not, why not just let the OS/browser on behalf of the user enable or disable dark mode, by choosing the appropriate CSS? Because as someone else has already pointed out, having the app "guess" whether I want to enable automatic dark mode or not, rather than just obeying my settings (perhaps I always want it on, regardless of ambient light?) is just stupid.