It's the genesis of the rifle... Many felt the same way when Glock introduced the polymer pistol... now everyone is in the game. From and engineering and ergonomics point of view, moving the bulk of the weight closer to the center line of the shooter, makes for a better handling and easier to use platform.
This allows the shooter to stay on target for a protracted period of time, without the fatigue associated with a traditional rifle platform. It also provides a full length barrel for higher velocities, and more impact energy, in a package that is typically smaller than a M4 carbine.
In the late 80's I purchased my first non-restricted AR-15 instead of a Steyr Aug (to save a few hundred bucks), and always regretted that decision. I've since sold all my AR's, and have revamped the collection with several non-restricted bullpup rifles. They are, at least for me, superior both for plinking fun, and for hunting. Nothing works it's way through the cramped and tangled forest better than these little carbines. They get dirty, or soaked with rain, they still function, and once back to camp, I stand em on the nose to dry out, and I'm ready to go after a coffee.