Barcelona don't want to pay what Saul wants for his salary, while Atletico can't pay all of Griezmann's salary. Saul considers better offers from other teams and Griezmann remains calm because Barcelona need him to leave. At the moment, Barcelona must amortise the remaining €72m from Griezmann's purchase. They prefer a swap to regain some of those millions so that they don't incur more losses (player + cash for Griezmann).