The problem is that historically, this is what's lead to tons of issues in games. Drivers make their own "optimizations" resulting in terrible performance for some task on one GPU, and great performance on another. Or instead of performance differences, it's outright bugs.
Then, combine that with GPUs being fairly expensive, and fast moving when it comes to new features. Most game studios aren't going to buy 20 different GPUs and test their entire game on all of them. So games often ship with terrible performance or bugs on various different GPUs. And it's often not the game's fault: are games really supposed to detect your exact GPU model, and change code paths to work around a driver bug? That's crazy.
To combat this, GPU drivers often get updates after a game launch that fix the issues with performance/bugs for specific games at the driver level, when it detects that those games are running. So now drivers become a pile of game-specific hacks, making the problem even worse.
This is the reason Vulkan is so low level. The goal is to make sure drivers don't get horribly bloated, and games aren't working around driver-specific bugs (they still happen, just hopefully less). And when games want to use specific GPU features for extra performance, instead of drivers trying to magically improve normal operations, they can make a vendor-specific extension providing the new functionality that games can opt into when the feature is detected (e.g., raytracing). That's part of why Vulkan has so many more extensions than OpenGL does.
Vulkan may be low level, but it's intended to be so. By foregoing Vulkan support, Apple rejected any attempt at making a higher level API on top of Vulkan that would work on every system. Instead, WebGPU has to try and abstract over Vulkan/Metal/DirectX12 separately, which mostly works, but leads to a whole lot of clunk and longer development time than if Vulkan was the standard everywhere.
That's not to say macOS should never have made Metal. But by not adding Vulkan support in addition later on, they're really hurting cross-platform compatibility. Sure, now Apple can optimize their platform to the best of their ability (theoretically). But that comes at a huge overall cost to the ecosystem, for instance with games having poor support for macOS.