I fear you have n idea what 3D printing is
These cages are made from Glass filled Nylon and knocking one up in your garage to the same quality and standard as one of these is not easy to say the least. I am a CNC machinist by trade so understand the requirements very well of working to tolerances of +/-0.1mm by hand and it is an art.
If it was that easy to do then would everyone not just do that rather than buying one? Either way everyone is entitled to their own opinion but thankfully for me these cages are proving a hit and I have orders to supply two UK race teams already.