It was for Chainmail, but they've now acquired the rights to D&D and are therefore retooling to the bigger property.
Ah, sorry. The rights history wasn't entirely clear in the articles i had seen
For the same reason he directed the first movie and was producer on the second and third - he still holds the rights. WB almost certainly got the rights only by allowing him involvement in the project.
That kind of follows. We can hope, though, that WB went, "Dude, we want the rights, but clearly from your last attempts, you kinda stink at this. We'll give you a producer credit. You get paid. Your resume will look great. But you will stand aside and let our people do the work." That would be nice.