why ALL INDIA RADIO of Visakhapatnam established during 70's occupied very big space, since then no further expansion took place.?

AIR has expanded into many other cities over the past 30+ years. It is expensive to build the necessary transmitters and infrastructure to support additional stations.

The Indian government was very short sighted when they granted radio frequencies, good for that frequency all over the country, instead of granting licenses local to the collective states and regions to various applicants. When the laws change that permitted independent companies to compete, it was bungled, similar to how it was done in the UK (similar oversight).

One more example of government not having sufficient foresight to properly govern an infrastructure and technology that they did not understand, and the interests of a few powerful people were influential in how things were implemented. Those interests are heavily protected and not easily changed at this late date.

The land that was set aside for their use is now private property, belongs to the operators of the station. If you have a concern, it needs to be brought to them, locally, not internationally. What happens to the land, how it is used or not used, is up to the owners of the land, not other people that do not own or control it.