Because gimmicks are not a bad thing, in any form of magic. They are not a "cheap" way out, they're not a demonstration of no skill. Gimmicks do not mean you are a bad magician. Gimmicks are for tricks that require a special device or method for achieving the effect that regular sleight of hand could not provide. You don't "just buy" a gimmick and instantly start performing: it still takes lots and lots and LOTS of practice. What younger magicians these days don't seem to realize is that gimmicks are not a magic genie that performs your tricks for you - it's a tool, JUST LIKE ANY SLEIGHT, to achieve an effect.
In CoinOne, as has been mentioned, a gimmick is used. So is sleight of hand in the trick. However, a gimmick doesn't need sleight of hand to validate it. They also teach a way of doing CoinOne without gimmicks, taught by Chris Kenner, called "The Deep."
The Deep is a fun routine, but it doesn't look anywhere near as impressive or magical as CoinOne. Because magic is about what happens at the end, not about how you do it.
Nobody but you cares how good your classic pass is.
On the other hand, everyone's interested when you do something impossible.
Honestly, most (non-professional / working ) magicians these days try to brag about their mediocre sleight of hand, oblivious that it takes YEARS AND YEARS to achieve such advanced sleight of hand - and even those guys use gimmicked effects. Reason being, they're dedicated to MAGIC, not showing off technique. They want to amaze, any means possible. And there's nothing wrong with using a gimmick to do that.