I never understood why they didn't use the Apple "UI". Where Apple presents fewer models (say N models), and when you select one, each is configurable for screen size/RAM/CPU/whatever (say K picks), yielding N*K possibilities, many Windows laptop sellers present a list of N*K SKUs where you need to triple check what the difference between SKU A and B.
They do. That's just the different base models. You can customize each one.
My guess is that some cell in an excel sheet says that some customers bought certain models in the past and no manager at Dell has enough weight or enough courage to question that and rule to NOT release a certain model.