RCC poles are used as their are aesthetically pleasing and blend in well in urban areas with streets with buildings.
RCC poles are cheaper. They can also be constructed at the site itself. This reduces the cost of transportation.
RCC poles also have a long life and require less maintenance. Sometimes, the concrete may chip and become porous. In such conditions, water may percolate through the concreate and reach the metal reinforcement. This can cause corrosion.
A downside is that RCC poles tend to shatter when a vehicle collides with them. This can be prevented with the use of PCC (Prestressed Cement Concrete) poles.