Natures do not affect IV generation during breeding. IV generation is random (and so are the IVs picked out by Destiny Knot). You are simply having bad luck, so keep hatching Bounsweet and you will eventually get one with a high Attack IV.
If one or both of Steenee and Comfey has a high Attack IV that you're trying to pass down, then you may find Power Bracer helpful. The Pokemon that holds it will pass down its Attack IV 100% of the time.
* Computers can't truly be "random" and the nature/IVs you get are subject to the game's RNG, but you don't need to worry about that.