I'm not sure what you mean by the "dart method". It sounds like you mean when you stroke the ball low like a draw shot but go even lower and skip the ball off the felt.
If that's the case, then the reason the pros don't use that method is because it is an illegal shot. The reason is that the cue tip remains in contact with the ball longer than a strike which is another form of a double hit. There are various rules which describe this. For example:
10.0 Jump Shots-Jump shots are legal as long as the cue ball is not struck under the center line that is parallel to the surface of the table. http://www.internationalpooltour.com/Rules/
FOULS-The cue ball is jumped entirely or partially over an obstructing ball with an illegal jump shot that scoops under the cue ball. http://en.wikipedia.org/wiki/Eight-ball#Standardized_Rules_of_Play
6.8 Push Shot - It is a foul to prolong tip-to-cue-ball contact beyond that seen in normal shots. http://www.wpa-pool.com/web/index.asp?id=121&pagetype=rules#6.8
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Edit: Thanks for the clarification. As a matter of fact, I've used that shot without realizing that's what it was called. My opinion now is that the dart method is more suited when you need more height (or more immediately) on the jump like when the obstruction is closer.
I guess in the end, it just turns out that most jump shots are only partial or longer distance where the cue stick doesn't need to be elevated as much and thus a traditional stroke would be favored since potting the ball can also be an objective so aim is more important. The dart method is probably best for simply getting out of a jam and avoiding a foul (thus perhaps comes up less frequently) when you need a high enough cue elevation where the traditional shot becomes difficult to pull off (i.e physically awkward).