Why do people lie?

To protect themselves, for self-aggrandizement, or to be mean.

For personal gain, to save face, or cover our footsteps. 

Besides the truth, the only way out of a lie is to lie a bigger lie. And the hole just keeps getting deeper. You cant dig out of a hole.

The truth always hurts

People have told lies to escape deserved punishment, to profit at the expense of others, to gain or maintain certain advantages, material rewards, or the praise of other humans.

Mostly because they were poorly raised by parents who didnt love them enough to teach them right from wrong. But also because they can.