Tire noise that gets worse over time is caused by misalignment. The misalignment is causing irregular wear, which is the source of the noise. And, of course, the worse the misalignment, the faster the noise gets bad.
But even a little misalignment can generate noise - it just takes longer. And that means even if everything is "In Spec". The published alignment specs are too wide - by half. The vehicle has to be within the inner half of the range for good tire wear.
Regular tire rotation helps prevent irregular wear - and therefore noise generation. Each corner of the vehicle has its own wear pattern - especially front to rear. Rotation forces the tire to wear a different pattern. Long intervals between rotations could result in a wear pattern becoming permanent - one that isn't substantially altered by moving the tire to a different wheel position.