maybe failed was the wrong wording, but they are all rucks or ruck/forwards rather than forwards
Correct and they're ruck/forwards rather than Fwds for a reason - at that size they will always fill a need to be part time ruck - jack of all trades master of none.
And you have nailed the reason there, generally blokes of that size will be playing ruck first and foremost, particularly at junior level. These blokes were all playing mainly ruck at u/18s. I've always felt that a ruckman that cant go forward is useless, but in modern footy with interchange restrictions the now defunct substitute rule even more so.
Bent Judge is also correct in saying that footballers are getting taller across the board.
While it may be true that very few players over 200cm have made it as KPFs, there have also been very few playes over 200cm pklayed primarily as KPFs and there are other sound logiucal reasons as why there have not been many.
The idea that 200cm is some magical number and once a player reaches that height he becomes incapable of succesfully playing as a KPF so is not sound logical reasoning, but narrow minded dogma.
As with anything the only rational way to look at it is look at each case individually, and if a bloke has the skillsets and attributes required why would you discount him just because he is "too tall"?
After all,
everything else being equal, a 205 cm forward is going to be harder to keep quiet than a 195 one.