I'm also a little confused as to why colorizations always aim to restore color to the equivalent of a faded color negative, with muted tonality and grain. Human logic is funny.Well, as a professional photo editor, you know that if the original b+w photo captures an image with say, a 50% grey value, you don't know if the original color was bright red, or closer to that 50% gray. Bright red has a much higher chroma value, but chroma isn't recorded in a b+w photo - color saturation is lost. Easily demonstrated by making an image in your favorite image editing program that's just straight up red, then changing the image mode to grayscale, then asking someone else entirely to guess the original color.
That, and I think the style is to mimic hand tinting photographs, where you would paint right on a b+w photo. The colors would look "faded" because whatever was used to tint the photograph needed to have a transparent medium, for the information of the photograph itself to shine through. That, and there's just so many colors you could use when hand-tinting. Back to our 50% gray. What if that was... bright yellow? You can't tint "bright yellow" onto a 50% gray area of a photograph. Yellow is highly transparent, and the grey would be too powerful to let its chroma value shine through.