In large part, that's happening because the soybean can do almost anything. Crushed into meal, it's a highly nutritious feedstock for beef cattle, which are increasingly being reared in confined environments rather than out on the range. Processed into oil, it can fuel vehicles in the form of biodiesel, or be used in any number of different industrial compounds. As a protein, it can serve as a base for a huge variety of food for humans, including (but very much not limited to) tofu and tempeh. Accordingly, demand is coming largely from Asian countries, especially China, which is expected to prioritize wheat production rather than soy over the next decade:
That's already been driving up soy prices, which has made it a more attractive crop for U.S. farmers, who've been switching from corn in droves. You might even say that soybeans are the chicken of the staple grains and legumes -- the birds are another big winner of the USDA's projections, having overtaken beef and pork long ago as well.