Would you like to buy a slightly used bridge - we in London have several you could have at bargain-basement prices?
Video cards have a design life of 8 months. By the time you have reverse engineered their stuff and made your own, you will be two generations behind for sure.
The real reasons are:
a) you wont just discover bugs, you will identify major cluster-fucks in the design.
b) you will discover they have lied and lied in the product descriptions.
c) you will find they have violated a ton of patents
d) two or three minor mods will treble the performance - and they are scared you could market their product as yours, out performing theirs.
e) they have used other people's IP with their permission, but not with their permission to disclose (requires additional fee).
Remember: Windows is clearly superior to the BSDs - the BSDs are desperate to steal Windows IP stack!
I have had to remove Nvidia cards from machines when installing Ubuntu over Windows, cos the installer wont even run in text mode on some.
Nvidia cards taste terrible, even with Peri-Peri source - even cockroaches won't eat them!