WotC tried to retroactively revoke an open gaming license that had been in widespread use since 2002. They had a legal theory why they could do this, but that theory contradicted quite a few public statements they had made on record. IP lawyers had very mixed opinions.

Many TT-RPG players enjoy reading rules carefully and figuring out fun ways to "exploit" them. So everyone jumped on WotC's changes and dissected the implications. And many companies in the larger ecosystem quickly announced plans to ship their own games competing with D&D.

WotC decided to back down and to just use Creative Commons, which largely resolved the immediate issue.