A clear distinction has to be made between following aspects:
1. Creating the raw file in a form, which allows a generic interpretation of the data,
2. Adding information, which is useful but not essential for the interpretation of the data.
DNG accomodates both concerns. However, one of the reasons (perhaps the main reason) for users sticking to the propriatory formats and to the propriatory raw processing software is, that most cameras offer features/options, which were/are not transformable in standard DNG format.
- saturation, contrast, sharpness. These are particularly striking, for many, perhaps most users wish to preserv and automatically use these in-camera settings,
- custom curve, like some Nikon and Canon cameras support,
- color rendering options, like "portrait", "landscape"
- exotic camera features, like Canon's Dust Delete Data, noise calibration, whatever.
ACR (and thus the DNG converter) did not allow for custom curves, nor for color rendering options up to the DNG version 1.2, which came out in 2008-05. Saturation, contrast, sharpness are still not covered. (*)
One can't expect customers to exert pressure on the manufacturers towards adopting DNG, while important features are not accessible that way.
(*) Saturation, contrast, sharpness are covered by Exif, but not adequately.