The various reasons for reducing the land under cultivation could be the following.
Actually, Indian constitution protects the agricultural land and that land should not be used for construction work. But perhaps there are many who convert the agricultural lands into developmental sites for benefiting in terms of money.
1. Conversion into private residential areas - apartments, houses, sites.
2. Laying of roads for the public transport. This is done by the government through acquisition of land.
3. Construction of industries. Due to industries, some land around that area turns useless and less productive. Water and air around that area may become polluted.
4. Too much of selfishness by people to grab the land, so that they could resell later in future after some development takes around that area.
5. To lay new railway track, airport, public corporation.
6. Inability of the farmers to cultivate the land for some years, due to some reasons.
7. Due to persistent drought conditions, the land may become difficult to cultivate. Often some floods and cyclones also turn some lands into uncultivated ones.