Good STL files are also a bit trickier to make than one might think. There's a lot that goes into making a STL that will actually print without tons of errors. It's not just so simple as to take a game model and convert the file type. You need to ensure the model is "watertight" and that the dimensions will ensure a print on certain types of 3d printing technologies. FBM printers will have certain minimum specs that are required for wall thicknesses and slicing, and in many cases, support material will need to be added to overhangs or areas of the model that might collapse during the printing process. SLS printing is self-supported, but there are still issues with thickness tolerances and scale, depending on the materials you are going to use. Not many modelers who use polygon-based modeling software understand all of this, because not every polygon-based modeling software has tools to check or inspect STL integrity, and it's much easier to create something that will fail with polygons than with NURBS or solid modeling or sculpting packages.
I use polygon-based modeling for most of my 3d printing models, but there were concepts about the process I didn't understand early on, and had to adjust my own modeling techniques to fix the shortcomings. Trust me, there's a lot of thought that needs to go into modeling for 3d printing and lots of considerations. Most of my models are intended for SLS printing, and I do not offer the models with support material. That would be up to the user to do with free software like MeshMixer. MeshMixer is excellent for analyzing the model for FBM printing or SLS. I usually put all my models through testing there before uploading, even though I do not use it for the creation process.
