Since the very reason given since the discussions began 15 or so years ago, Nvidia, and most of its competitors (Intel being a special exception for an unrelated reason) have always said that due to fears and concerns about reverse engineering, they - Nvidia and ATI, now AMD, have been slow and limited in making available any documentation or assistance that could directly or indirectly ease reverse engineering of its technology, its intellectual property (IP); not to Open Source / Free Software developers, but to potential and current 3D video card competitors.
Providing the direct firmware blobs, even if encrypted (to be decrypted in memory on the video card) does reduce the effort of a reverse engineering attempt. Perhaps legal or senior management has overruled the previous plan to make encrypted firmware blobs. I believe there was one or more blogs entries written about methodologies of bypassing the decryption of encrypted firmware blobs even when/if the decryption key(s) are secure stored in the Nvidia GPU, or at least recovering the decryption key which undoes a lot of work by Nvidia, and may cause violate terms of various patent / IP licensing agreements.
Nvidia could possibly go out of business if they were barred from obtaining necessary licenses allowing them to implement video codecs in hardware in their future products.
I suspect this, or some benign reason (Nvidia's Linux developer were simply busy with in-house development, or on holiday) is the culprit.
* Unrelated pure speculation:
My pet theory about why Intel has been so open with their open source driver support for Linux, is that it is intended to be a) to support their APU processors and b) to try to help AMD in its secondary market (video GPUs) rather than their primary market (x86 compatible processors) which Intel knowns AMD needs to keep being a viable option, as AMD's x86 processors alone the past few years could of easily drove it out of business.
To avoid more anti-trust violations / investigations Intel needs at least one viable x86 competitor to remain alive. Preferably neither too far ahead nor behind, so that Intel continues to dominate the CPU manufacturing sector, it has at least something that is realistically a potential threat to their business. Just not a strong potential threat. But by possibly supporting AMD's secondary product line by providing an open book to their GPU's documentation and interface via their driver source code, Intel can provide a subtle nod to technologies, or other solutions that AMD could re-implement to improve their (AMD's) video card offerings.
In summary Intel can stand to help AMD in their video cards to keep AMD alive, which serves a critical purpose to Intel, as Intel needs someone that can be seen as potentially a rival CPU manufacturer.
Regarding Intel's domination of microprocessors:
While ARM processors have shipped in record numbers the past few years, they are manufactured by various companies who pay ARM a royalty (per unit made AFAIK), so Intel remains the single largest designer and manufacturer of CPUs. Although ARM Inc. has experienced explosive growth and tremendous profitability, it is still a tiny company in relative terms, such as market capitalization (a common benchmark) compared to Intel.