So the lawsuit and the development started roughly at the same time. To me, it looks like if there was any chance of getting H&W's input on Dragonlance, it went up in smoke when they sued. I know Hickman consulted for Curse of Strahd, so I wouldn't be surprised if WotC started DL development and intended to get input, then the lawsuit started and they decided "Naw let's not, let's do it ourselves only."
An alternative theory is that WOTC cancelled Margeret and Tracy's book trilogy (despite Book 1# being written) because they had given them permission to write it before developing their new Dragonlance IP that the book contradicted.
Because they didn't bother to tell them they were making a new Dragonlance IP.