First, they would spill all of their secret sauce for others to "draw inspiration" from. And there is a lot of expensive secret sauce in there. Not all of it is protected by parents either; more on that below.

Second, they would make it a lot easier for competitors and patent trolls alike to seek litigation. One of the criteria thech companies have for filing a patent is how easy is it to detect when it is being violated. Open source your stuff, and you make it much easier for the competition to detect any violation.

And it is not like these companies are violating patents intentionally; much the opposite. But there are only so many ways to implement Vulkan or DirectX, and completely independent teams will come up with similar enough solutions, and with broad enough patents, that there will be overlap every now and then. That is why they file patents in the first place. Only the high cost of litigation and the risk of mutually-assured destruction keeps legitimate vendors from rattling sabers more often.

Then you have NVidia with their immense investment and advantage on the software side, from the CUDA runtime to countless libraries like CUBLAS and cuDNN. That investment goes much beyond a relatively simple Vulkan/DirectX driver.

So the question is less "why don't more of them open-source userland". The question is "why do any of them do it"?

Source: former insider with enough patents under my belt that I lost count.

Any conference talk schedule at one of these conferences (https://gameconfguide.com) will prove the point of how little they care.

It is all about gameplay, taking advantage of gaming IP, franchaises, how to squeeze the ultimate performance out of specific hardware, user engagement,....

You will find an occasional talk about open APIs, probably even done by some Khronos folks, and that's it.

> Moats were excavated around castles and other fortifications as part of the defensive system as an obstacle immediately outside the walls.

Unfortunate wording?