[lovlar]

Making a good mechanical design is difficult, it usually involves making several iterations which in the physical world takes a lot more effort than iterating on software.

One thing that always bothered me is that most people with 3d printers seem to design things on their own from scratch and rarely take on others designs, improve them and share them. There is little collaboration going on for 3d prints in comparison to software. Except from maybe ~10 widely successful projects that now have healthy communities improving them.

Why is GitHub and similar sites not used more among makers?

[imtringued]

You're assuming that CAD tooling is mature enough to enable that.

There is no standard format for CAD projects/design files. STEP is a standard format for exporting finished designs.

There are many CAD-with-code platforms, but none of them converged on a shared language the same way there are multiple competing C compilers.

I might be beating a dead horse with this one, but standardizing around FreeCAD isn't possible either, because it isn't good enough to compete with commercial CAD software like Solidworks, OnShape or Autodesk Fusion. Blender is almost there though, but for mesh-based free form 3d modeling.

Then on top of that, a 3d model on its own is useless. You need to manufacture the part. Printers have varying capabilities and something that has turned out to be particularly essential is multi color printing, since it allows embedding text and markings onto a print but not every printer is capable of doing it or doing it economically.

Ordering individual parts is expensive, which means you'd rather buy a full kit from someone who is getting volume discounts.

[latchkey]

In your first sentence, you answered your question.