The idea behind the frame taking so long to build, yet the robot itself being pretty much instant is... Well, the frame is the robot, you spend 20 seconds machining all the raw materials together, and building the frame.
then you spend half a second to insert the correct programming and tool.
Also keep in mind that there's all different kinds of config options, that's just the default, not all have tools, not all have brains, you can have a T2 made out of a T1, or not.
What exactly would you want this "Robot building factory" to be able to build, and what would make it special over a standard assembling machine?