Why?........Just a hunch, but they obviously want to keep up with the competition by coming out with the magnums, so it wouldn't be that much of a stretch, and something that could save them a lot of time and money in the long run, not having to deal with all those fittings, and shipping and handling charges.
Mainly it's just the way most successful companies grow, and that's by improving their products.
Maybe not, but that's just my hunch, and just an opinion like everyone else!