Because the range is abysmal, and about to get worse. They're fun to screw around with, but practically useless in high-end content. Getting in the face of one target usually means getting in the faces of all the bad guys, because they tend to clump together. That's not normally a good idea. And getting close to a boss is pretty much suicide ... They all have a OHK stomp of some kind. Fusion rifles are a far better and more versatile option for close to mid range.