Just because files can be downloaded for free doesn't mean that they're not copyright protected. Do your research before using these files in commercial projects. 3D printer files are digital files ...
Hosting models somewhere and putting a buy button in front of the download is certainly a solved problem, but after spending some time buying and printing a variety of non-free 3D models online ...
I have several 3D printers ... over to the custom printer. I should note that Klipper, I think, appeals to people who like tweaking settings and editing configuration files.