For many many years the only reason that Linux has had any attention _at_all_ from Nvidia and ATI is because of the professional workstation market. These people think nothing about dropping $2-3K on graphic hardware. They have no problem having their developers work with Nvidia and ATI and pay a lot of money for NDAs and special access to ensure they get the features that they need. Without this market there would be no proprietary drivers from Nvidia or ATI.
I remember very plainly from the bad-old-days of ATI were people were forced to hack binaries firegl drivers to make them work on consumer ATI devices. FireGL being the professional workstation line of cards. It sucked, but the hardware is mostly the same so it worked. (Not much has really changed.)
ATI has to deal with competitive forces and until the 'linux professional workstation' folks are satisfied with the API support in Gallium3D drivers then ATI will need to continue to pour resources into Catalyst.
Then they are required by law to keep portions of their software secret. Thanks to DMCA and friends. Combine these things together and ATI really has no choice.