There are a number of factors that are often credited with causing a push for universal white male suffrage during this time. Here are a few of them:
- The Revolutionary War. Obviously, this happened long before 1820, but the values expressed in things like the Declaration of Independence helped cause a desire for white male suffrage.
- Growth of the market economy. As this happened, people began to understand that things that government did mattered to their everyday lives. These included things like the creation of banks, the imposition of tariffs, and the building of internal improvements like canals.
- The rise of slavery as an issue. This (which first showed up in the arguments that led to the Missouri Compromise) made many Americans, especially in the South, think that politics might be important to them.
Basically, then, the idea is that there were more things going on that made politics seem important to the average white man. These things made him want to have the right to vote so he could have a say in the government that ruled him.
If you have access to The American Pageant by Bailey, et. al, read about this at the start of Chapter 13, entitled "The Rise of Jacksonian Democracy."