Because big, greedy mega-corporations forced us to! That, at least, is the pat answer you'll find (expressed either implicitly or explicitly) in most major-media pieces on the subject. It's an answer that belies a shocking ignorance of our food history (as well as basic economic principles like supply and demand).

Flash back about 125 years in America and you'd find a nation of cooks who, just like today, wanted/needed fats for various purposes: baking, cooking, frying, spreading on toast, that sort of thing. In those days, different fats were favored in different regions of the country according to price and local availability. In the wealthier north and northeast, where dairying was common, people used a lot of butter. In southern states, which were far poorer, people used a lot of lard.

Liquid oils were largely unheard of then, because extracting oils from seeds was a laborious, and therefore very expensive, process. Solid fats were the order of the day. The problem was that they were often quite expensive. Butter prices fluctuated even more wildly then than they do now. As for lard, it wasn't uncommon, depending on market conditions, for the fat on a pig to be worth more than the meat. Rancidity was also a big problem for both types of fats, which prevented them from being kept very long, or being shipped very far.

Things began to change when technology made it possible to start extracting large amounts of edible oils from the germs of seeds (notably cotton seeds). However the end product was a liquid oil that most Americans were ambivalent about, in part because they had very little flavor, but mostly because they weren't as versatile as solid fats. That changed with the invention of hydrogenation. Crisco (crystallized cottonseed oil) was invented by Proctor & Gamble in 1911, and was considered something of a miracle at the time. It was not only solid, it was cheap and kept at room temperature for up to two years.

So, it wasn't very long before shortening began to cut severely into lard sales. Soybeans were introduced to the U.S. in the 30's, introducing another abundant source of vegetable oil into the market. And then of course, in the 50's and early 60's, medical studies linking animal fats with cholesterol and cholesterol with heart disease, began to be published. It was the death knell for lard in most of the first world, and not coincidentally, the time when ad campaigns like the one I put up two weeks ago were launched by desperate meat packers. All was for naught, however, as lard quickly faded to semi-obscurity. Shortening and margarine (the hydrogenated alternative to animal-based butter) were ascendant.

Which pretty much brings us up to where we are now — with lard, perhaps, poised for a reversal of fortune. Of course it's doubtful that it'll ever return to its former prominence, liquid oils being so prevalent now. But who knows? We may be entering the new Great Age of the Pig.