AMD separated HDCP and DRM related silicon from video acceleration units some time ago to be able to open source their GPUs completely sans the NDA bound stuff. Even this is a very big generosity and step from them for the Linux community.
I'm sure that the firmware contains some highly proprietary and revealing information about some of their secret sauce. So, they won't be able to do it even if they want to.
Also, if the core enablement and configuration is done in the firmware, some vendors may find themselves in a hard position, since they may be selling crippled GPUs as lower spec cards.
Last, but not the least if folks enable faulty CUs in their cards and see the faults, they may create some (albeit unjustified) noise in "teh internets", which will return as bad press.
So, while the firmware is good for research and educational purposes, it's also a Pandora's box IMHO.
In the end, opening it up isn't any worse than opening up the kernel driver to begin with (you could apply similar arguments to that). And AMD were OK with it, and from what I've heard, DRM is really the main issue here. As usual, media lobby poisoned the technology for us.
I'm a big free and open software advocate. I primarily use free and open source software, and try to open every line of code I write. I'd like to see the firmware on the open like the drivers. I just wanted to talk my understanding of hardware. If my comments sounded otherwise, I'm sorry, my bad.
BTW, I'm not employed by AMD or ATI. I was just one of the independent members while the GPU driver beta testing was closed to outsiders.
DRM always complicates things, but always get broken at the end. Also, it's always a crippling pain.