I think that the willingness to shoot in a player is determined mostly by the driving skill.
A player with high driving will take better shots than a guy who's not good at making space for himself to shoot, so he's more likely to shoot the ball.
It happens in real basketball, and to me is the best explanation.
Of course the shooting skills are important (a guard with low JR won't take many 3s, especially if using LI or low post), but I think that the driving skill is the most improtant in determining the player's willingness to shoot.
Anyway there are too many things to consider when talking about this: offensive scheme, PG's passing skill, driving, defender's OD\ID skill, defensive scheme, player's passing ability (if a guy can't pass the ball he's more likely to shoot it... watch this player of mine
(9278837), he aint got a high DR skill, but his passing is really low, so he takes a lot of shots... he's a good shooter so he often makes them though).