I agree the surface finish is rubbish. But I am talking about small quantity stuff, often for personal use. When I fab boxes from scratch, whether it is wood, aluminum or other materials the result is often not commercially appealing. When I stuff everything in a project box the same answer holds. It will be years, if ever, before 3D printing competes with molding for commercial external parts. Unit costs, surface finish, material selection - there are a myriad of ways in which it doesn't compete.
If surface finish really matters, filling, sanding and painting are options. In my shop the surface finish of even the commercial boxes is poor because of all of the dings from tools and other rough handling.