"Tales of Monkey Island was developed by Telltale Games, under license from LucasArts." - Wikipedia
"Does Lucasarts know what you're doing? Answer : Of course they do! (Monkey Island is a LucasArts property, after all.) We licensed the Monkey Island rights from LucasArts, the same way we've licensed other franchises from their owners—like Sam & Max from Steve Purcell, Strong Bad from the Brothers Chaps, and Wallace & Gromit from Aardman—and now we're working closely with them to bring you this new chapter in Guybrush's adventures." - Tales Of Monkey Island FAQ
It is quite clear Telltale licensed Tales Of Monkey island , but it is not known if they "bought" the license. Either way , they made a sequel for the MI series , so why say a FT sequel wouldn't be possible?
I cannot ask Tim Schafer why he doesn't buy the FT license, but it is his game , and he made it quite clear that it is his favourite work of all time.
@Origo : Full Throttle has a huge potential as a saga , and Tim Schafer is the only one that can come up with ideas to continue his work. Nobody will be able to do it better than him. Maybe we will remind him and Lucasarts of FT with our fangame. Let's just make it happen.