Yeah, one reason to buy films reels, even if you have no immediate use for them, is the save them from "cutters".

But yeah, projection prints technically belong to the studios, who loan them out to theatres and expect to get them back. Private ownership is not really kosher, but it's saved the studios' bacon quite a number of times, as the private collectors often take better care of "their" property than the studios do (e.g. when the studio has effectively destroyed its copies, and then wants to make a home video transfer). Star Wars is just another case-in-point.