Because windows map sdr contents to srgb color space. Which nobody except designers uses. Most monitor today ship with a much brighter and, high contrast, vivid

Because windows map sdr contents to srgb color space. Which nobody except designers uses. Most monitor today ship with a much brighter and, high contrast, vivid color profile by default. If you toggle your monitor to srgb color profile. You should see a color that looks really similar to sdr contents in Windows hdr mode. In my opinion, I also don't like it. But there is surely no way for Microsoft to chose a color profile that looks like without toggle hdr on given there are so many monitor manufacturers in the market. I think chose the most safe srgb option is understandable.