Why did humans evolve to be hypocrites?

Social-desirability bias. When the truth doesn't sound good or can be easily misconstrued, we lie and then cover up that lie with thick layers of cognitive dissonance.

People want to be and to remain socially accepted, and some have found it more advantageous to speak a big game than to actually back it up. Conscientousness as a personality trait is not evenly distributed throughout the human population. Whether that's mostly nature or nurture is beyond my level of understanding.

It's always been like this

As soon as you develop moral standards, you will never be able to live up to them fully, so yeah

Animals are, too. They eat other animals, yet don’t want to be eaten themselves, so...

Religion and/or politics.

My dog is like that too 😒