IMHO it is because the doubles have a reputation as short range guns and lots of people believe they hype of the gun sales people and think that by buying a B/A magnum they will be able to kill any deer at 500 yards. Whilst the truth is most of them couldent hit a barn with a shovel if they were standing inside it.
Again IMHO most should indeed get a "short range" gun and stick to shooting at living creatures less than 150yds away.
This is not a dig at any of the posters here, but a general observation from what I have seen on numerous ranges up and down the country.

Regards