Because if Salah leaves and they do worse, which they probably will, then every fan will be incredibly mad with the ownership for sending salah away. So Salah has all the power to strong arm the team into getting a good contract, he can do whatever, and to be fair looking at how he got paid, he hasn't been paid that much money for most of his time there, just recently he has been paid fine, but early on he was paid very low.
Liverpool fans will of course encourage the club to retain Salah, even though he is no longer young. Moreover, if at the end of the season Liverpool is able to win prestigious trophies such as the Premier League or Champions League, it is certain that Salah will get a short-term contract from management. There is a lot of speculation regarding Salah at this time, the Saudi Pro League club is also reportedly interested in recruiting him at a fantastic price.