Another thing to remember about the #OGL is how I think it was shaped by two events of the '90s.
First was the start of Wizards of the Coast. The Primal Order, their first product, resulted in a lawsuit from Palladium Games because they included conversion appendixes for a variety of RPG systems. (TPO was a "capsystem" product meant to be added on your game of choice.) This is exactly the sort of thing that people are now claiming is obviously fair use. It was not so obvious, Wizards well knew!
The threat was so grave and existential that a new corporation, Garfield Games, was formed just to publish Magic: The Gathering, so that it could get investment that would not be threatened by the possibility of the whole company being destroyed by the Primal Order litigation.
After the TPO suit was settled out of court, Garfield Games was merged into Wizards of the Coast. The people who ran WotC in 2000, such as Peter Adkison, know personally how much water the "this is fair use!" argument
held in actual pragmatic fact for a publisher. All it took was one game company to decide they disagreed that it was fair and were willing to file suit over it.
The second event was the near bankruptcy of TSR. Again, key people (such as Ryan Dancey) involved in rescuing D&D from the implosion of TSR by facilitating its sale to WotC, had that experience to inform the creation of the OGL. It was not impossible to imagine D&D being owned by some corporate entity that did not care about it;
business owning work for hire had unwound, or no one had saved a paper trail of rights ownership/transfer. (Can you tell if it's work for hire?) As with fair use and game rules, there was a big difference between theorizing about the legal status of some work and putting your financial well being on the line by seeing if anyone will step forward and assert a right to sue you about it.
The OGL was a way to ensure that core RPG mechanics of D&D would be available to future generations --
regardless of whether they already are via fair use (yet to be tested in court), and regardless of what may be the future ownership of related copyrights. Stop the uncertainty.
Make games. Create things. Share them. Know that when you are hit by a bus, your asshole cousin who inherits your copyright will not have grounds to sue the guy who added your novel Prestige Class to his game world for sale as a PDF on DTRPG.
I disagree that it is revocable, and I don't think any rights are given up because the SRD contains zero product identity. Product identity designation is a carrot to encourage publishers to use the OGL without fearing that they were giving up their original content.
So why do it? Peace of mind. Safe harbor. And a way to pass it forward by designating OGC that others in turn can use.
@mcv Something else maybe to clarify.
Nothing in the SRD was Product Identity. So if you were strictly deriving from the SRD, your chain of copyright only included (1) the OGL itself, (2) the SRD, (3) your Open Game Content.
The ONLY possible Product Identity involved is that which you yourself designate to guide downstream licensees. Anything that COULD be product identity and COULD be covered by Fair Use is NOT Open Game Content in your chain.
John Nephew
Martijn Vos