Doesn't seem like Sporting have been working that way. Seems we've "reached agreement" at least once, only to discover new demands.
When there's little trust it's no longer worth much to concede to the latest round of brinkmanship.
Sporting certainly want the money on the table and United are no competition. We can privately run our alternatives again, and be ready to walk away. As far as Sporting and Gyökeres are concerned, we can delay the transfer at which point pressure starts to move to Varandas.