Well people are not honest because they have personal interest and motive and in order to get it they need to be dishonest or anything whatever it required.
This is correct, people tend to lie because they have some motives for doing that or maybe it is their job. To do such things to get what they want.
There are still people who lie for no reason. It's some kind of sickness. A person is lying and can not stop. I saw such a person. He contradicts himself and constantly confuses facts