Because of the price and the fact that there is no real need for a civilian to use one the only reason a regular guy would have one would be just because its cool. In my opinion its only real need is as a sniper round.
So "just for fun" is no longer a valid reason to have a gun? Heck, many of my guns are just for fun guns. I have a few hunting guns, and a few defensive guns, but many are fun range toys....