And some skaters will learn triple jumps easily and for others it will be an extremely tough ordeal. Some skater have an affinity for spinning, others hate it because it makes them dizzy.
You might be predisposed more or less to a certain activity. But that does not mean that you aren't able to acquire the relevant skillset.
And none of us actually know what is going on in Czisny's and Kwan's heads. How much of their success/failure was down to environmental and how much to personal factors. How much they did or didn't work on their mental skills, whether in a formal or an informal setting.
And how much of their success is down to good/bad coaching.
As far as Czisny is concerned, I'd guess that technical issues play a very big role. She has always had horrific jumping technique. It has been slightly corrected but is still terrible.
Pretty hard to land jumps consistently when even at her 100%, they are rather
.
Most people seem to perceive physical fortitude as something that can be easily trained with enough effort but they don't perceive mental fortitude in the same way, when exactly the same logic applies there as well.