Specifically for EI over Chairman's is the emphasis that your team's mission is to inspire engineers and increase respect for engineering. While your Chairman's submission is judged on to what extent your team is a role model team in outreach, conduct, fundraising and really all aspects of your team, I think EI is more about how you use your team's resources to really go out and bring some STEM awareness to the community, so really you could win EI with a rookie outreach team, but you couldn't win Chairman's with one, since sustainability and history don't seem to be defining factors for EI vs. Chairman's.
Just my 2 cents
