The Central Government was considering the proposal to amend the Anand Marriage Act, 1909 so as to provide for registration of Sikh Marriages therein. However, pursuant to the direction of the Hon’ble Supreme Court in the case of Seema Vs. Ashwani Kumar, reported in AIR 2006 SC 1158, most of the State Governments and Union territory Administrations are taking necessary steps to make all marriages compulsorily registered in their respective States/ territories where such marriage is solemnized irrespective of religious denominations. Giving this information in written reply to a question in the Rajya Sabha, Shri Salman Khurshid, Minister of Law & Justice, said that having regard to the position of law as contained in Hindu Marriage Act, 1955 which is applicable to Hindus, Sikhs, Budhist, Jainas and other persons who are not Muslims, Christians, Parsis and Jews and that Section 8 thereof covers the registration of Sikh Marriages within its ambit and that secluding Sikhs from other categories of person may invite similar demands from other religious denominations which would go against directive principle contained in article 44 of the Constitution. Hence, no separate legislation for registration of Sikh marriages is considered necessary, Shri Khurshid said. (Link)What they're saying is that by giving Sikhs their right to marry under their own act of law, it would open up the door to other minorities asking for similar rights. I guess Shri Khursid is afraid of more work.
And India wonders why Sikhs have issues with the state. If I was Budhist or Jain, I'd also take great exception to this.