If your phone freezes, you're almost certainly the unlucky person who got a defective CPU or ram. Generally speaking, Linux (the kernel) doesn't freeze; when there's a freezing bug present, you know it. It happens frequently.

There just aren't that many rare states the kernel gets itself into. Video drivers are notoriously hard to get right, but a bad video driver would affect everyone.

Manufacturing process isn't perfect, and chips can become marginal over time. These failures are frustrating because they manifest as random bit errors, or complete clock-stopping events. Sometimes the various SMPSes are weak and undervolt with sufficient load or a weak battery. Sometimes the clock skew is just sufficiently low to keep things running until a sudden temperature spike causes one component to miss a step.

The worst part is that these random failures are so hard to reproduce, it's almost impossible to make a warranty claim.