Possibly because they wanted their jobs back. Back in the day, employers hired and underpaid immigrants and therefore firing white people that were paid more. Since immigrants accepted less pay, for the same work done by a white person, white people wanted the immigrants to be fired so they could get their jobs back.
You also have to accept the fact that racism was a wide issue back then. Americans usually treated people of other cultures and ethnicity’s very differently. Also, lack of religious tolerance was another problem. For example: Jehovah Witness’s children were kicked from schools around the 1930s to 1950s because their religious conscious wouldn’t let them salute the flag and saluting the flag is a pagan ceremony in which people give adoration and admiration to the flag, a certain type of idolatry that the Bible condemned and many years before that, Jehovah Witness suffered prosecution in the US for teaching other people Bible principals. Same thing happened to people who were Chinese; people who are Chinese believe in ancestors and have certain traditions and because many of them weren’t part of popular religions they were bullied for it.
