Sony's most consistent and profitable division is their financial services division. Gaming is far from that.
At its current state Sony Pictures and Sony Music are consistent profit generators for the company while the rest of it is in flux. Spider-Man happens to be Sony's biggest movie franchise next to the Bond films (which they share with MGM). Other than that they don't have any big active movie franchises. So there's absolutely no reason to expect Sony to want to sell their biggest franchise away. The only reason they would do that is if the company is in dire financial straits and need a cash infusion. Or they undergo major restructuring that requires them to sell off their entertainment business.