Under Voltage & Over Voltage Protection

Is it because whoever designed the system determined that there is no need for them?

There are under & over voltage sensors around which when incorporated into your Main Switch Board, UPS & Generators controls will protect your equipment.

There are also Voltage regulators available to trim over voltage and UPSs support under voltage.

Regards,
Sapper

Such protections are normally provided at the LV sub stations of the Utility supply systems/ Industries /Commercial complexes etc.Hence, same is normally not required at the down stream distribution net work due to economic reasons.

However, if the concerned appliance is expensive/critical (eg.medical appliance),necessary protection is ensured through UPS by making uninterrupted and quality power supply available to the device.

By controlling the HV you control the LV so its in place.

A supply company has limits within which it must supply - voltage Hz etc.

Not warranted on a cost-benefit analysis. But, having said that, for important equipments it is normal to provide the above protections too.