I'll put it in simple terms. Over the past 5 years, the value of the Panthers squad has increased significantly, so they've to shed players to stay within the cap. At the end of 2019, they moved on two of their highest paid players in RCG and Maloney to upgrade others. And each year since, as they've upgraded Edwards, Luai, Yep, Leota, To'o etc from modest contracts, they've offloaded established players and recruited middle of the road guys like Sorensen, Eissenhuth and Garner to fill their squad.
The Roosters, on the other hand, almost never lose players of the calibre of Kikau, Koroisau, Luai or Crichton due to cap pressure. RTS, Mitchell, Manu and Suaalii all left/are leaving for personal reasons. Far from losing players to manage the cap, the Roosters recruit established stars like Cronk, Tedesco, Crichton, Smith and Leinu.