People already spend thousands of dollars on skylights without any professional lighting design, yet they pay a professional draughtsman to design it specially

People already spend thousands of dollars on skylights without any professional lighting design, yet they pay a professional draughtsman to design it specially for their house, council to approve it, and licensed tradesman to build it. I don't get why they don't spend those same thousands on what you suggest or an off-the-shelf product that an electrician (or DIY) can install.