30V is classified as safe voltage for humans, higher voltage may cause serious damage to your heart and may lead even to death.
As you probably know, for high-humidity environments such as showers, saunas, or swimming pools, electrical lighting operating at 36V AC is also used for the same reason - to ensure human safety.
Additionally, most electronic devices are designed to operate at standard voltages such as 3.3V, 5V, 6V, 8V, 9V, 12V, 13.8V, 14.4V, 18V, and 24V. Therefore, a 30V range covers the needs of nearly all such devices with a small margin.