And this is precisely what anti-trust ligitation would allow them to do.
Preventing someone from reverse-engineering a product with the sole intention of maintaining monopoly status may be seen as anti-competitive.
AMD makes really, really good CPUs now, but only after ligitation against Intel allowed them to keep up with evolving x86 standards.
It's not about being "arsed" to build your own, the problem is NVIDIA can add to CUDA at any point in time and launch a new GPU at the same time and the market will buy them because the cutting edges of the ecosystem are all CUDA-based, so people are forced to buy NVIDIA if they want to stay on that cutting edge and not wait a year for AMD to reverse engineer it.
What ZULDA did wasn’t to maintain a compatibility with the CUDA API and provided an open implementation of it but rather use all the CUDA based libraries that NVIDIA provided on top of it.
The equivalence again would be that not only Google implemented their own Java compatible API but rather that they used the now Oracle owned JVM to do so and redistributed it.
AMD already implemented CUDA essentially one to one in the form of HIP in ROCm. The issue that they face is that they don't have all the equivalent middleware to make copy pasting code actually work and this was what ZULDA did but instead of building a HIPdnn they just reused NVIDIA binaries.
If it was a clean room implementation of the API NVIDIA wouldn’t care. Heck that’s exactly what AMD did with HIP.
But what you cannot do is essentially intercept calls to and reverse engineer NVIDIA binaries in real time because you can’t be arsed to build your own.