Was discussing the whole big men not being able to shoot FT's issue the other day with a friend for an hour trying to really pinpoint and understand why it has in fact been and continues to be a consistent problem.
It really can be explained very simply. It all has to do with what that player's particular niche was when they were growing up, which obviously had a lot to do with their height. For example, if the player was naturally taller than the competition in HS or college, he would often not need to develop an above average jump shot in order to dominate the competition. This phenomenon becomes more apparent with height --- all things being equal, 7 footers need a jump shot much less than a player who is 6'5 who needs a jump shot much less than a player who is 6'0, etc. In short, if you don't "need" it, why develop it?
To bring this point home, shorter players often cannot take advantage of their height to play effectively, and therefore, a jump shot is often necessary. For example, CP3 being a 6 footer was probably the shortest player on the court during his time in college, and presently in the NBA. Therefore, as previously stated, he needs exceptional shooting ability.
But what about taller players who can shoot? This has to do with the position they played growing up. If one played SG because they were shorter in elementary/HS, they would be equipped with a SG skill set. If this same player had a growth spurt, they would often be placed as a Center with that same skill set (i.e. Nowitzki). This phenomenon can also be seen with undersized big men --- if they were the tallest of the bunch in their younger years but failed to sustain that relative height, they would be equipped with post skills at a smaller stature relative to other big men (i.e. Barkley, Chuck Hayes).
There's also a rather large proportion of "late bloomers" who start playing basketball at an older age as the player approaches 7 feet. This late entry into the sport definitely can be correlated to the lack of shot development.