Essentially, I want to know if the copywriter can or should help us craft our 'why'.
Quite simply, no. A copywriter cannot do this for you. In addition, your use of the words "us" and "our" is a red flag for me. The entire team together ALSO cannot craft this story.
It may feel good to use we/us language to signal that you are a team, but the stories that emerge that way are typically "design by committee" exercises in business vision/strategy. One person -- a founder, preferably the CEO -- needs to dictatorially define the vision and the why and persuade others to his/her way of thinking. Maybe not in long-form copy. Maybe in the form of a keynote address with slides. But the person offering the why has to truly own the story.
A copywriter can help you cast the story into a form suitable for an About page, but that's secondary. If you don't have a single dictatorial visionary who can tell the story, you have far bigger problems than a website About page.