OP answered the Julia-specific part but I'll chime in with a solid, language-agnostic yes, there are still reasons a GPU dev might want to target specific hardware. GPU hardware at the moment is more vendor-specific than CPUs. Off the top of my head, major differences include specialised hardware like Nvidia's tensor cores, differences in common hardware like cache and register size, and niche features like Nvidia's combined grace-hopper machines or AMD's gpu-cpu hybrid MI300A.

Sophisticated high-level approaches (like Julia's) will be able to utilise/mitigate some of the differences but I don't think we're fully vendor-agnostic quite yet (and probably won't ever be at the evolving cutting edge).