Regarding market sudden fall

If any negative news is there prior to one day how market(nifty) falls so rapidly. I know sell orders are placed but who buys it? (there is a negative news then also who will buy in premarket order).
Please explain me how this takes place on bourses like NIFTY & SENSEX?

Those who sold earlier would buy to book their profit.


People who think that prices are available at a bargain.
People who want to contra-bet. (hoping market will reverse)
People who SIP. They buy regularly no matter whether prices rise or fall.
People who shorted and now booking profits.