Self-interest/motivation has its own MO. Also, sometimes motive isn't so important - physical behavior is. This is the evidence which can be collected. Otherwise you can't really assume much. Your original comment seemed to imply a conspiracy though through "built by".

This is a little detached from the original context though, and there's another issue there; People are not random processes, they may choose to pursue selfish strategies conditional on being in a system where it is uncritically "assume[d] people are being reasonable by default".