Trying to explain why people often seem to act against their own (long-term) interest can be a daunting task… Wikipedia actually lists 172 cognitive biases!
While we study how they affect human behavior and therefore how policies could be optimally designed to face “biased” behavior, understanding the reasons and causes of such behavior could be a first interesting step. Indeed, evolutionary economics try to trace back features to the evolution of mankind and find some convincing arguments in some cases.
See for instance Jonathan Rowe’s very interesting article on evonomics.com