Honestly? Because that upper had the Rail Vertical Grip already on it and the whole package seemed to work. Generally, I tend to run Larue Hand Stops on my carbines, across the board, so those styles of grip worked well (and was California-friendly while I was there) but the RVG end up providing the same form factor. I also like having something that I can push against a barricade, as that's a common shooting position that I run into.
*Note, that's not me in the picture, though I shoot it the same way.
I had an ATPIAL-C on that upper for a bit, to try out the ergos. It worked well. Personally, I've found that if you need to make room for a laser and a light, a side-mounted light (3 o'clock) with a pad and the PEQ on top worked, but if you didn't need the laser, a 11 o'clock setup with a push-button worked as well. Like this:
I don't own NODs, though, so I can only talk to shooting in unaided night conditions.