Why all political parties supported OBC Reservation Bill?

Lok Sabha on Tuesday passed a constitutional amendment bill to restore the powers of the states to make their own OBC lists, with 385 members voting in its favour and no member opposing it. The political parties which are creating ruckus during the whole monsoon session, have united on the OBC Reservation Amendment Bill. But why did all the political parties came in support of the Government over the OBC Bill, watch?