It's pretty easy to understand. Your opponent usually has to adjust to your opening as opposed to you having to know an open Sicilian. In Grand Prix formations black usually ends up fianchettoing his/her Queen's bishop, which many Sicilian formations don't do. Now if your opponent plays a Dragor or an Accelerated Dragon they won't mind this at all.
The louse stats are probably due to the fact that a lot of the Grand Prix games you will see in databases are between higher rated players 2200+ The Grand Prix is one of those openings that is used by players on the lower end of this rating scale (2200) to keep out of the book lines of their much stonger opponent (2400+), many times we are talking about 100-300 rating point difference, so the person with white had a good shot of losing the game anyway.
In other words it's perfectly playable as white at the sub 2200 level. I've gotten good positions from it in the past. Don't let database statistics influence your opening repertoire choices too much, most games in these databases are between very strong players and our "truth" isn't neccessarily theirs.
The Grand Prix Attack gets a lot of votes as an alternative for an attacking player. Is is sound? Is it fun? The wins-draw-loss percentage isn't stellar: 33/24/43 (%)
...but that kind of statistics is hard to evaluate unless you know the ratings of the players.