Of the merkins contracted for next year, only five of them were there when Robinson won his second premiership in 2018 (and only four of them played in the grand final). NRL clubs have a fairly high turnover in the space of five years. Look at the Storm, only six merkins still there from their 2020 grand final side, plus four backups. That is two thirds of the squad gone in less than three years (we have 11, including Blake, who were in our NRL squad in 2020).
Unless relationships sour with the key players there's no 'getting stale'. This would be a big part of which players the club vigorously fights to keep and which ones they don't. You need your playing group to get along as well. Dudes who don't fit in get rissoled pretty quick. Many of these never really fit in anywhere and become 'journeymen'.