If someone breaks or looses a component there are four main options:
Buy a replacement item to replace the item which is broken, or missing a piece.
Search online and hope someone has already designed a replacement part which is available for purchase.
Measure, and design their own replacement piece, then "3D print" it.
Most people do not have the skill needed to complete option #4. Unless the piece is a block with a hole in it. If we're talking about something more complex like a curved battery compartment door for a remote control, they are not going to succeed.
Even a "simple" feature like a 1/2-13 UNC threaded hole is going to be a huge hurdle for the majority of CAD users. Most "thread" tutorials show a simple triangle swept along a helix. They never mention how to determine the correct dimensions and tolerances so the thread will actually work with another existing part.
Another factor to consider is the generally poor quality of printed parts obtained from most home printers. They are getting better, but the printer, and the materials themselves can't create the fine features which are present in many injection molded parts.
The printed materials while often "true thermoplastics", don't have the same mechanical properties of the original part. Not to mention the color will be wrong too.
Cost is also a factor. I might spend $5 for a real replacement part. Or I can spend a few hours in CAD, then send the part out to be printed on a professional quality 3D printer for $50. Then I can spend a few hours sanding/finishing/painting the replacement part....
Someday this might be a factor. But this is the same claim they've made for the past 30 years.
I agree, until the spare parts CAD library is readily available it's going to take far too much time and effort to recreate the CAD file.
There are some pretty impressive scanners though that can pick up that geometry pretty quickly (another up front cost), which saves you some time and then you can always have that CAD file ready for when that part inevitably wears out again.
In our last GrabCAD Meetup we actually showed off that capability of the scanner to create a CAD file for 3D printing here
I agree, until the spare parts CAD library is readily available it's going to take far too much time and effort to recreate the CAD file....
Scanners and photogrammetry are great for capturing shapes. But, they are rarely usable "as captured" for making replacement parts. Holes, rough patches, misaligned bodies... they need to be repaired prior to printing.
The time and skill needed to repair the data is often less than that needed to create a 3D model when armed with a pair of calipers and other "traditional" reverse engineering tools, but the time needed to make a good mesh/part is still a large hurdle.
And don't overlook the cost. "Good" scanners are still $10,000 or more. And paying someone else to scan a model is not cheap either. They have to pay off that bill somehow.