Let's try make sense of the Dybala situation before we start cussing the management. Firstly, Paratici would never agree letting Dybala go without any capital gain unless Sarri told him Dybala won't be in his plan. How Dybala can't be in Sarri's plans? Here's why:
1) Sarri likes to play a lone striker upfront in his system with Higuain at Napoli and Morata for a time being until Jan at Chelsea then re-signing Higuain in the window. We all know Sarri doesn't rotate much so having Lukaku and keeping Higuian will be enough in his mind. Since Mandzukic can't offer upfront as he used to, Lukaku will be the younger alternative upfront.
2) This is what Sarri said in a press conference last week:
Sarri says Ronaldo is the only player in his side with the license to "be free on the pitch".
Following their
3-2 defeat to Tottenham in the International Champions Cup, the new Juventus boss praised the Portugal captain, claiming that as one of the world's best players he should be given the freedom to be as creative as he can.
"Cristiano is the best player in our team, of course," Sarri said. "So I think that we have to organise very well the other 10 for the defensive phase. But Cristiano can go everywhere on the pitch. He is the best player and I think that for him it's very important to be free on the pitch.
Sarri has stated Ronaldo will play in a free role while the other 10 players follow his instructions. It worked for him at Napoli with Dries Mertens and Eden Hazard at Chelsea with both players having their best seasons under him. You think Dybala should suit in a free role given he is at his best when roaming in the attacking third but Sarri chose Ronaldo in that role so that leave Dybala with not much option regarding first team opportunities.
3) This benefits only Manchester United. The manager at the club has no use for Lukaku as his shortcomings will only hinder his team. Lukaku openly wants a move to Italy but given the financial situation this only leave Inter and Juventus as his only destinations. Conte always wanted Lukaku as he tried to buy from Everton before United trumped him in summer 2017. He is back in management with Inter this time and trying to get him once again only Inter can't offer what Utd demand. Instead of wasting time with Inter, this proposal works in their favor as they get one of the best attacking players in world football while offloading an unwanted asset.
So in short, the reason why the Dybala-Lukaku has become ever likely is because one does not fit with Sarri's vision while the other does and Inter can't agree on Utd's valuation.