But the point of coding the choice is ... so the user has a choice? This is a bizarre response.
This would still remove the visitors ability to say "I want THIS SITE to be in light/dark mode", without affecting all other sites / apps on their system. This page could support reading from the browser/OS, while still giving the choice on top of that.
Again, this choice was probably implemented ... to give the user a choice.
Some people may not want everything to be light or dark mode. I am one of them.
Some articles may not work well with dark mode.
Like someone above said, some sites implement it as an after-thought. In my case, I'm giving more love to dark-more because there are simply more nice color combinations in dark more than with white.