Once again, contrast issue. The background cannot be dark because then less finished projects attract more attention. Make the background white.
There are factors other than brightness that bring attention to an object. In fact, in your avatar, my eyes are drawn to the red hair more than the black clothes.
The black in the progress bars is easily identified as the background, while the bars are clearly the foreground. The mind tends to pays less attention to a background than it does a foreground. However, more importantly, the bars stand out more because they are a changing entity, while the background is static.
If 0% had a black background while 90% had a white background, then yes, it would stand out more. But because they all use the same black background, it plays an insignificant role in contrasting the different progress levels.