There are cases where you want tons of random numbers (e.g. monte carlo) and the line between "good enough" and "disastrously bad" is often unclear. Providing cryptographic random numbers is the only possible API that's both safe and generic.

As the post says, it's worth entertaining the idea of having the kernel provide a blessed way for userspace to do that, though I admit I've never personally seen a scenario where RNG was truly the bottleneck. But it'd still be nice to kill all the custom RNGs out there.