Short answers, pulled from the story.
The Game System License was released on the 17th of June 2008. This document was introduced by Wizards of the Coast to allow external creators to build products compatible with Dungeons & Dragons 4th Edition.
The Game System License prevented anyone using it from publishing under the old Open Game License. It also included a clause that allowed Wizards of the Coast to update the terms unilaterally and required licensees to pay the legal costs of Wizards of the Coast in the event of litigation.
Green Ronin and Necromancer Games refused to participate in the Game System License. Clark Peterson of Necromancer Games declared the agreement an unmitigated disaster and announced his company would cease efforts to support the new edition.
The Game System License drove out nearly all third-party producers for the short-lived 4th Edition. Only Goodman Games and Mongoose Publishing signed on, and even they found little benefit in doing so.
Andy Collins, who served as the Design and Development Manager around the release of 4th Edition, later admitted that he had argued hard to retain an open license similar to what Wizards had done for the 3rd Edition. He expressed doubt about the decision and wondered if it might have been better to let the Open Game License die.
The decline of the Game System License was sealed by the release of the 5th Edition of Dungeons & Dragons in 2014. The 5th Edition returned to the Open Game License model and rendered the 4th Edition agreement obsolete.