The tire sounds are way less at low speeds. Where the sound matters for safety is where people are and around corners and situational changes. These moments tend to be where speed is Low and varying. As well of the type of sound. If you hear a revving engine come towards your direction you pay it attention.

This is why it is useful for cars to make sounds. It also is the reason why that sound is so annoying. It is a constant trigger for our brains to react.