It's not really a trademark issue - WotC has a trademark on D&D, particular styling of that, and other stuff like Beholders. They also hold lots of copyright on

It's not really a trademark issue - WotC has a trademark on D&D, particular styling of that, and other stuff like Beholders. They also hold lots of copyright on stuff that is explicitly not (and never was) under the OGL - the setting of the main D&D adventures and books, for example. They probably can't copyright the idea of a playable race of Orcs or Elves, likely can copyright (and license) particular descriptions or art of those races, and maybe can copyright the specifics about how those races work. It isn't clear, because this all hasn't been tested in court. Spells are another example - is a spell like "Lightning Bolt" with particular effects something that can be protected by copyright? It didn't use to matter much - anyone could just add the OGL to their publication and be fine - but it might start mattering a bunch more.