Because they don't respect the United States and how a country as great as this can give them the opportunities to make a successful life here. It's the "Gimmi, gimmi, gimmi syndrome."
It is exactly because the people who come to our nation to settle use so many languages that it is necessary to use one language as a basis of unification of the people. Having a common language and culture gives a country its national character. The diversity of the people gives the nation texture and spice but the basis of strong unity has to be at the base. Without unity as Americans (not hyphenated Americans), there is no nation, just random competing micro-societies.