Why does the government put taxes on commodities?

The CTT or Commodities transaction Tax is levied on Trades created on Commodities Exchanges the same as Securities transaction Tax – STT on Equity Trades. it is a tax payable to the Central government by commodity traders and therefore categorized as a regulatory charge.
CTT was first introduced in 2008, the proposal faced with vigorous opposition from commodity Exchanges. They disputed that commodity trading in India was at an emerging stage & introduction of CTT might unfavorably affect them. therefore the plan was withdrawn.
CTT was proposed again the Budget in 2013, however only on Non-Agricultural Commodities like Gold, Silver, Aluminium, crude oil among others. now the Bill was passed & CTT was levied on Trades in commodity Futures on 1 July 2013.