I really think and get the feeling that because Andy and Salah are leaving, that the Liverpool front office and FSG want to start something new. They want to begin a new era of football and one of the best/easiest ways to do that is to sell or allows players from the previous generation to leave.
Alisson is an odd case too, because he is still a world class keeper (when on the field), although I'd argue his distribution of the ball has dipped a bit as he's entered his mid 30's. He's always had moments in games or seasons of either disaster or near disaster with the ball at his feet, but he would also reward you with an out ball that was pinpoint leading directly to a goal, but I digress.
His situation is unique though because of the fact that he is aging, and nowadays he is going to miss upwards of a dozen games a year it feels like. On top of that he's been very outspoken before about not wanting to play forever (like Neuer) and that he's interested in either going back to Roma or even to Brazil to finish out his career. That to me screams he doesn't want to play much past 35, if at all, and would like to do it at a place where the pressure is significantly less. Thus, this is a pretty prime time to move on for both he and Liverpool imo.
It is a ton of guys moving on, but unlike last summer, this summer will be moving on from guys that are aging, don't play as much as they use too, and don't quite fit into the future of the team. Last summer I felt like was selling to make money.