> Aren't patents public?

Yes. Patent literally means the opposite of latent (hidden).

Kodak comes up as the assignee name in ~22000 patents in the USPTO (search at [0]), only counting since 1976, so certainly incomplete. Of those, some have been superseded, some are worthless false paths, and some are incredibly valuable. The patents may be public, but nobody is going to give out the other information for free.

[0] https://patft.uspto.gov/netahtml/PTO/search-bool.html

Edit: I forgot that patents are only valid for 20 years, but at any given moment there were still likely to be thousands of valid patents.

The ultimate significance of the patents contained within the portfolio (how they will empower business plans, why they may be quite valuable) will not necessarily be apparent from simply looking at the technology described. And a potential buyer would always want to keep these hidden things (essentially its own business plans) secret.