There are several reasons why people immigrate to the United States and the United States allows people to immigrate to the country but they need to file few forms and go through a legal process to get into the country. Those regulations and the US immigration laws are strict and people who file petitions to immigrate to the country will have to wait for a long time to get their visas and to get into the country. Generally, you can immigrate to the United States, if you have married a US citizen or if you are a skilled worker. You can also get into the United States for some other reason but all the applicants who file petitions and who have good reasons to immigrate may not be issued visas as soon as they file their petitions and there is a numerical limit and only a certain number of foreign nationals will be allowed to immigrate to the country, every year. And due to the numerical limits, foreign nationals will have to file their petitions and wait for years to get into the country.
Many people do not wish to wait for a long time to immigrate legally to America and so they immigrate illegally. Many undocumented immigrants in the United States are unskilled workers and they choose to get into the country illegally because there is no other way for them to get into America legally. Such people enter into the country illegally as they feel that the living conditions in the United States are better than their native countries and they believe that they can earn well in America and support their poor families. Many others also choose to get into the country illegally as the legal process through which they can immigrate to America legally is longer and also due to the visa processing fees. Instead of waiting in queues and immigrating to the country legally, they just cross the borders illegally and get into the country, sooner.
Many people get into America illegally, just because they do not have anyone to sponsor them for lawful status in the country. The United States issues visas to skilled and unskilled workers but the number of visas that the United States issues is not sufficient. People who get into the country on non-immigrant visas also overstay their visas as they feel that they may not be able to get into the United States and remain there permanently if they leave the country. Many Mexicans, Asians and people from Central America immigrate illegally, due to economic reasons and some immigrate to avoid political oppression. The United States is one of the most desired destinations for millions of foreign nationals and many dream to get into the country for better employment opportunities, to reunite with their family members and to provide better lives for their children and hence, there are several reasons for immigration and for illegal immigration.