Why, given the intense media pressure which comes with a Ferrari drive, would Hamilton accept a drive alongside Ferrari's new young star who has just been given a (very) long-term contract. LeClerc is the future at Ferrari.
There are several other drivers who would be a better fit - Nico Hulkenberg, who had a Ferrari contract only a few short years ago, but which was never signed? Jean-Eric Vergne, who has a test/reserve/development contract with Ferrari? Kevin Magnussen, who already has close links with Ferrari due to his Haas contract? Kimi Raikkonen?
Ferrari need a wingman for Charles LeClerc until Mick Schumacher is ready.