-The manufacturers dont make their real money with having copyrights on technical documents. In contrast to book authors or musicians.
Yes, but they are still exposed to liability from the use (or misuse) of their documents, so it is reasonable to expect that they would like to control the distribution of the documents, and reduce misuse.
Cessna did provide many "Information Manuals" which were a "frozen it time" reprint of the aircraft flight manual, and suitable for study, and groundschool, but not the "official" flight manual with which to fly the aircraft.
-In the interest of safety, the most current documentation of any aircraft should be easy access, but barely ever is.
"Current" is an important element. Flight Manuals, as well as maintenance manuals in particular, are subject to revision, or to being serial number specific to an aircraft. So again, one could possess a manual which seems to be close, but it not entirely applicable. As long as the pilot (or maintainer) realizes this, and does not misuse the document, all is well, and yes, having the information "out there" increases knowledge. But, when people start flying and maintaining with out of date or non applicable manuals, problems can begin.
This can be particularly troublesome when an aircraft has modifications with Flight Manual Supplements, and changed limitations, or restrictions imposed by AD, resulting in Flight Manual changes. That information has to be available to the pilot. It will be missed if the wrong source Flight Manual is referenced for flight.
So study with whatever you can find, but assure that flight is conducted with the specific Flight Manual (and supplements) applicable to the aircraft.