If you look back through history, the root cause of major social reforms in the United States was the Great Depression of 1929. Prior to that, most Americans were self-sufficient and fiercely proud. The Great Depression changed all of that practically over night.
There were a number of other factors that were already beginning to develop, most notably the failure of a number of businesses just prior to the stock market collapse in 1929. However, the actual collapse set into motion a domino effect that would be felt throughout the entire world. Several banks failed, resulting in millions of people losing their entire life's savings. Many factories closed, resulting in lost jobs, and a number of farms went into foreclosure, resulting in a decrease in the production of food. Local governments started facing collapses because they couldn't raise any tax revenue to keep their own programs going due to the fact that so many people no longer had any money.
To make matters worse, the government voted to hike tarrifs, resulting in other countries responding by raising their own tariffs. Suddenly nobody wanted to buy American goods, and Americans couldn't afford to buy foreign goods. This ended up resulting in a world-wide depression. In 1930, over 4 million people were out of jobs, and by 1931, that number had doubled. As if this wasn't bad enough, the Midwest experienced a devastating drought about the same time, resulting in even more farms failing and a number of people being forced to migrate to other states looking for work, placing an even greater burden on those local government.
When FDR was elected, he initiated a number of government programs focused on relief, recovery, and reform. Since Congress was controlled by the Democrats, he had no resistance in enacting his programs. New welfare programs were created, Social Security was introduced, and a number of job programs were initiated. All of these things combined helped to poise the United States for a major recovery, which happened to coincide nicely with the outbreak of World War II. The United States was just beginning to redevelop a strong workforce, and they had a number of countries suddenly wanting to buy their goods.
After or during World War II, many of these programs were dissolved, but many others ended up growing into the social welfare programs we have in such great abundance today. Sadly, the job creation programs began to disappear, but the "handout" programs remained. Over time, they have become so ingrained in our country, it would probably be next to impossible for any form of government to ever eliminate it. As a result, the need or desire to be as self-sufficient as their ancestors has bgan to dissipate with subsequent generations.