It’s fractions of a fraction of a fraction of some metric.
Like Shabazz Napier is absolutely a superior point guard - of all the point guards on earth, in terms of skill, perhaps there’s a handful better than he is….but he’s a fraction too slow or just fraction off athletically and you can’t be that in the NBA. Like he’s 99.90% of the way there, but the tip of the spear is so pointy that there’s no place for him.
It’s like when fast NFL guys think they’re going to race professional sprinters. They’re really, really fast, but the pro sprinter is 100% and his 100% is going to absolutely thrash your 99%.
This, plus there is an inherent mental ability that is its own form of intelligence, an ability to interpret what they are seeing at high speeds and react in centimeters or even millimeters in ways that others can't. I read an article years ago about Michael Jordan that talked about his genius ability to read speeds and angles, to know when he was open, and know when he had to relocate. To know the exact moment and distance when to turn the exact angle and arc so he would get to the basket a split second before the help rather than a split second after.
I have coached a lot of youth and some high school aged basketball, both boys and girls, and the mental aspect is so underrated and so often missed by coaches at all levels who almost always go for the athletic measurables when they put their teams together and think they can coach the mental up. I am not talking classic mental toughness when I talk about this kind of mental acuity, I am talking the ability to see how a chessboard with 10 moving pieces is developing just a little better than everyone else that is on the court.
The first thing most high school and even many college coaches do when they organize their lineups is to put the best athlete among their short players at point guard and put the ball in his or her hands every possession. Some of these players can get coached up to be decent point guards, but I think the mental ability to see the court this way is an inherent component of a person's makeup just like their speed or jumping ability or height, and I do not think coaches appreciate that fact. You can coach a kid up a little on it, but either the player has it or they don't.
I also think shooting is such a unique skill, and it is also fundamentally a natural ability of a person to instinctively be able to judge, in a split second, the distance to the basket and proximity of defenders, and release the ball with the right force, velocity, arc, and rotation to consistently put it in the basket. I read a story almost 30 years ago where a reporter claimed that Pat Riley said that Greg Anthony could take 1,000 shots a day and he would still never be a good shooter. I absolutely believe Riley said that, and I also believe that statement is 100% accurate. Greg Anthony was a hard worker but was never going to get better as a shooter. I know Anthony had a couple of decent percentage shooting seasons on Portland late in his career, but he was deep bench and taking about three catch-and-shoot 3's a game, and a lot of his minutes came in garbage time. That was not scalable.
Maybe 5% of kids I have coached who really put the time in ever materially improve their shooting, and I suspect there is some similar metric as you move up the pyramid of talent. Name the number of UConn players, men or women, that arrived in Storrs unable to shoot and became great shooters. I am sure there are some, but I can't think of any. On the other hand, Brian Fair may have been the laziest player to ever get meaningful playing time on either UConn team, and he was in range and accurate when he walked in the gym. Fine motor skills like shooting are mostly baked in, and just how the players' minds and bodies work.