by 
People are lazy.
Why else would we avoid responsibility? Yes, that was a judgmental statement. People are not as lazy as they may appear. It is more likely that people avoid responsibility to avoid rejection, to avoid vulnerability, and to avoid embarrassment.
Historically, people needed to be included in the tribe in order to survive. Being expelled from the tribe would likely result in a death sentence. Therefore, acceptance in the group became a matter of life or death.
This fear of exclusion has extended into a fear of taking responsibility for mistakes and a fear of consequences to avoid rejection. People resort to tactics (thinking errors) such as blaming, minimizing, making excuses, or justifying in order to exempt themselves from responsibility.
This often has the opposite of the desired effect. We start to lose trust and respect for the person who repeatedly offers these thinking errors and refuses to take responsibility for their actions.
Conversely, we respect the person who admits to mistakes and offers to remedy them. We feel safe with this person and can trust them.
People have the capacity to be forgiving when mistakes are admitted and corrected.