Compared to CUDA, Vulkan is... not fun to code compute in! The serialization bridge and duplicating data structures and functions between CPU and GPU is tedious.

I hear both CUDA and Vulkan are not fun to code in.

But yeah Vulkan is famously verbose. It takes about 1000 LoC to draw a triangle

CUDA is very much fun to code in!

Nvidia provides devs with great tools (Nsight Systems and Nsight Compute), so you know where you have to optimize.