I don't know why it's never been re-created anywhere since, but if I were to have an educated guess, there are a few factors I think are responsible for it, some of which you've touched on:
I agree with you that he probably isn't all that adaptable, and that he has that in common with most managers. I also agree that he's done well to have such longevity in the game, and that not many survive in coaching this long.
(I
would suggest, at this point, that it might be better for him to move to a DOF role, as many managers do at his age / stage of career, but I don't
want to suggest it, because I think that suggestion would be met with hoots of derision from large sections of this forum, who would gleefully impart to me, that his personality/character/mindset/skill set would make him totally unsuited to that role!)
The other factor(s) which I think might be responsible for not re-creating the success he had earlier in his career, are probably either pandemic related - both the world and football have changed a huge amount since the pandemic, so that a manager like CW probably finds it difficult to operate as effectively in this changed reality; and then there's the possibility that he was personally severely affected by some aspects of the pandemic, as many people were and continue to be. Obviously the pandemic had a greater impact on some than others, depending on what happened to individuals and their loved ones, and how that's affected their lives going forward, and, as I said in another post, the apparent state of CW's mental health and wellbeing prior to his leaving in 2021, possibly hints that might be the case with him, although I'm just surmising.
And the other factor is simply his age. I think any managers whose successful teams are 'greater than the sum of their parts', 'team spirit' 'die for 3 points' teams, burn out much sooner than managers of teams with highly talented individual players, because the 'die for 3 points' way of managing, demands much higher energy than the calmer, more considered, 'managing individual talents, tactics and coaching techniques' type of management. To be clear , I'm not suggesting that 'die for 3 points' managers don't engage in tactics and coaching techniques - I'm sure they do, but they've got the added, high octane, 'die for 3 points' aspect to deal with as well, which probably leads to burnout at a younger age.
(And, yes, I'm aware of the irony of me quoting Warnock's "die for 3 points" to describe a high octane style of management, that leads to earlier burnout, when I know full well Warnock himself carried on managing far longer than most managers - well into his 70s, I think. But I think Warnock's an anomaly in this, as he is in a lot of things - he's very much the exception, rather than the rule.)
But as I say, that's just a best guess on my part, as to why it's not been re-created anywhere, since. Let's hope he proves everyone wrong, and suddenly re-creates it with us for the rest of this season
and the next, and we go on an amazing run, win the play offs, then spank the Premier League's ass next season, and end up in Europe! I can dream!