Why do people cast their vote through a secret ballot?

A secret ballot was used earlier for casting a vote.

The voters were given a white sheet, and they would write the name of the candidate to whom they would want to vote and put that pair in a ballot which was confidential. It protects their identity as all the votes were mixed and then counted.

But nowadays electronic voting machine (EVM) is used to cast a vote by pressing button against the party the voter wish to vote.