My completely unsubstantiated guess:
the club wants Lukaku back. He's one of the highest scoring strikers in the league the last couple of seasons, was once a Chelsea player and "loves the club". Conte probably wanted someone else, but he was told that they'd go in for any big player Conte wanted in exchange for bringing Lukaku in and that player is Sandro. The only reason I'm thinking this is because there was no talk about Sandro coming here until the Lukaku rumors started to look more promising.
Or maybe Conte believes a big, power striker is what this team needs.