This space wallpaper is a deep-field image obtained using the Wide Field Imager (WFI), a camera mounted on a relatively modestly sized telescope, the MPG/ESO 2.2-metre located at the La Silla ...

As to why Microsoft is charging 99 cents for the pack it is likely to do with licensing. Last I checked, Microsoft is not operating a deep-space telescope, and such images in 4K are rarely free ...