They haven't learnt their lesson from Coutinho yet.
Even if they could meet a price we're willing to sell him for (which would be a ridiculously high amount), theres no guarantee he'd be as good for them as he is for us. He fits our formation and style of play perfectly... I daresay he'd be good for Barca too... But no guarantee he'd be AS good.
As good as Salah makes Liverpool look at times, I think Liverpool is also making Salah look good too. He's perfect for us, but I don't think he would be perfect for everyone.
My prediction:. If/when the sad day ever comes that Salah leaves us... He won't be as successful at his next club. Like Coutinho.