Well, I'm really only stating the obvious here, but the reason would most likely be that the two sides are too far apart on contract demands v willingness to pay. Reports are, and who knows how accurate, are the sides are not close. If they were, it would be a different situation.
Not saying it won't get done but it seems like the Tua camp is fairly adamant about getting what they termed "market value", and Grier has a history of preferring not putting huge guarantees in contracts to allow future flexibility.
If neither side "blinks", nothing can get done.
Which side do you think "blinks"? Or do you think both sides are just posturing and the sides are closer than they appear like a rearview mirror?
I would also point out that those other deals (Burrow, Lawrence, Herbert, etc) got done a year earlier, as soon it was allowed by rules to do so. That is apples and oranges.