When I was much younger I didn't understand the concept of people who never had to deal with clients having a dress code but now I sorta do: the company is trying to create or promote the concept that everyone in the company is a member of the same team and have more in common with each other than they do with outsiders. Whether or not this actually works I don't know, but that's the only thing that makes sense. Same reason I guess the military puts everyone in camo these days, even people well behind the front lines.