One good reason is that it's not always obvious who has the rights. Even if the copyright holder is clear it can be hazy whether there might be outstanding NDAs

One good reason is that it's not always obvious who has the rights. Even if the copyright holder is clear it can be hazy whether there might be outstanding NDAs and licensing deals that would cause problems. So it's usually safer and (importantly) cheaper not to bother. You need either an insider keen on their own initiative to open it up, or a powerful PR reason to do so. It's a shame, but probably unavoidable. I think we ought as a society to at least dramatically shorten the copyright period for software (it's obvious that something like the patent system's 20 years would be more than sufficient) but I can't see much chance of it changing. > Will these sources die somewhere and never be revealed? :-) Sadly, yes, mostly. :'(