The suitcase is a brand icon that extends well beyond just the cart. Bonobos’ shipping boxes are also suitcases/briefcases. For any current customer, there would likely be an immediate understanding of why that icon is used.
In progressive agencies, where the lines between functions and departments are blurring, the brief is often a joint effort among the planners, creatives, account team and an involved (in a good way, we hope) client.
Something a lot of agencies just don’t execute well yet.