Very interesting!
The search results evidently come from a variety of authors. Quite a few repeats, some without pictures. But the rest seem to fall into two groups; novel parts and re-creations of existing parts. A few of the existing parts are things I have searched for (yellow fences for modern house, seat for front of covered wagon, pirate ship mast rings) and perhaps the creators of the 3D prints were frustrated in their attempts to locate the parts elsewhere. Some parts beg the question 'why?', such as red System X connectors and traffic cones: surely these are cheaper from DS?
I wish someone would set up a scan-and-print service (perhaps they already have?); you send them a part and they send you one or more exact copies, plus the original one returned. That is a service I might pay for!