I would think the contract he's under now is probably the reason he will stay for another season.
Mane is really not worth the, say, £28m they'd need to pay to get him. I like him a lot but I think United would be bonkers to spend that kind of money on Mane after one season in the Prem and I think they won't.
Hoping it's a bit of a PR ruse on their part to muffle their own transfer failure today.