Short answers, pulled from the story.
Wizards of the Coast released the Open Game License in the year 2000. This legal document allowed third-party developers to modify, copy, and redistribute game mechanics from Dungeons and Dragons.
Open Game Content includes core mechanics, rules, and procedures that anyone can use. Product Identity protects names, logos, stories, and specific character traits that third-party publishers cannot use.
Leaked documents suggested that Wizards of the Coast intended to replace the Open Game License with version 1.1, which would have imposed severe restrictions on third-party creators. The draft required creators to report revenue exceeding $50,000 annually and pay royalties for those making at least $750,000 in income.
The company released the System Reference Document 5.1 under an irrevocable Creative Commons license to end the attempt to deauthorize the original Open Game License 1.0a. This decision followed a coordinated movement where over 100,000 people signed the #OpenDND internet petition.
Ryan Dancey spearheaded the initiative and modeled the license on the open-source software movement. He argued that embracing these ideas would spur a huge surge in independent content creation.
The license created an immediate boom in the role-playing game industry with the majority of new entrants adopting the d20 license. Electronic publishing allowed creators to reach a wider audience and sell their products at a higher rate than non-d20 products.