Because greedy mega-corporations forced us into it! Or anyway that’s the pat answer you get in most of the pieces you read on the subject. It’s a simplistic idea that ignores the big food and technology trends that were underway at the time, as well as basic economic principles like supply and its effect on price 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 lard on a pig to be worth more than the meat.
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 when Procter & Gamble went to market with Crisco — crystallized cottonseed oil — in 1911. P&G had been using cottonseed oil as an additive in candles and soaps for years, and hydrogenation was a hot new technology fresh off the Continent. Put the two together and you got a vegetable-based fat that was not only solid, it stayed fresh at room temperature for two years. More than that, it was significantly cheaper than either butter or lard. Quite the miracle product for the time.
Thus 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, bringing another abundant source of vegetable oil into the market (and driving down shortening prices even further). 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 this one were launched by desperate meat packers:
All was for naught, however, as lard faded to semi-obscurity. Shortening and margarine (the hydrogenated alternative to animal-based butter) were ascendant, and for a lot of very good reasons. 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.