yea the thing is, although the shot may be made under "phycological" pressure, compare this to a "real time" opponent engagement sport, where the kick, or pass has to be made whilst under mental pressure AND under physical pressure from an opponent trying his darndest to gstop you from doing what your trying to achieve.
same with shooting and darts, you are not under any direct pressure from your oponent to make your own shot. Darts, and snooker can be practised as is in controlled confitions and you just have to repeat the same actions time and time again where your opponent cannot stop you. these cannot be practised to anywhere near the same level in team/oponent based real time interaction sports.