Printer Service Manuals should be free

I’ve been fixing quite a few printers lately.  Lexmark, Xerox, Samsung, HP..they are all there.  What I find interesting is if I wanted to get a service manual for that particular printer, I can’t go to the manufacturer’s site and download it.  There are a few sites out there that offer service manuals but there are many hoops to jump through.  Plus, I don’t trust all these sites.  I understand that most people don’t need service manuals but why should they be this big secret?  I never understood that.