I really had to think about in order to answer your questions well and honestly. I think a lot of it stems from just never quite being a fan of the traditional rifle form. There is something inflexible about it and it just doesn't quite work for where my hand likes to be. For this reason I've tried bullpups but tended to like the pistol carbine format the best - and it dawned on me it was because of the grip and hand position.
Let's add into it that, although I don't do it much any longer, I've been into airsoft for about 5-6 years. Yes, I am a grown kid who likes going into tactical situation with people shooting at me while full well knowing I am not going to actually die from a bullet. I've played a bit at HVA in Carmel, NY if anyone is familiar. In playing airsoft I got my hand on almost every replica of a tactical weapon. In doing so I really came to like the AR15/M4 platform because of how many options and accessories are out there.
So combine all of the above and the EVOL seemed to fall into place as a universally expandable platform. I can use my grip of choice, stock of choice, foregrips, AFGs, vertical grips, bipods - and I don't have to think "Will it fit?" because the platform is standardized.