From Pew Research: The naturalized citizen population in the U.S. continues to increase rapidly. The total number of naturalized citizens in the U.S. almost tripled between 1995 and 2019, from 7.6 million to 22.1 million. The share of lawful immigrants who were naturalized grew steadily from 38% in 1995 to 65% in 2019. Net result: a greater share of foreign born persons in the U.S. are citizens — thus able to vote.
there are about 46.6 million foreign born persons in the U.S. (legal, illegal, temporary, permanent) –up from 34.2 million in 2000.
Green card holders can achieve citizenship after a waiting period of at least five years before they are eligible to apply for U.S. citizenship. If you are married to a U.S. citizen, you may be eligible to apply for citizenship after three years. Once one applies for citizenship, the bureaucratic steps take about a year.
Pew says that immigrants are more likely to be naturalized if they speak English very well, have strong ties to the U.S. and have lived in the U.S. for a long time. (To pass an English test, you must be able to demonstrate an understanding of basic English grammar, vocabulary, and reading and writing skills.).
My sense is that many immigrants from Mexica and Central America are relatively less motivated to become American citizens due to continuing strong attachment to their countries of origin.