Why and how was the delhi plundered by the British after 1857?​

After the revolt it's resources were drained and it's system of administration was altogether changed.Following points will help to understand this question better:
After the revolt of 1857, Bhadur Shah Jaffar was sent to Rangoon jail for rest of his life.

• His sons were butchered on the gates of the Red Fort.
• His successors were declared as mere Prince and they were thrown out of the Red fort.
• Queen Elizabeth was declared as the Empress of India by the Queens's proclamation.
• Indians were declared as unfit to rule themselves.