This is also further encouraged by the welfare systems of the western societies they infest and infect. One man, several unofficial wives (in the eyes of the westerners), and each getting money for kids as if they are single heads of households.
When they stop making it financially profitable and feasible to do this and make them have to pay, the numbers will decrease. It will not stop, even with illegals, unless and until that practice is stopped.
And that practice will not be stopped because of the number of Mormons who hold federal office. Nothing against them just stating a fact They are dependent on their constituents to keep them in office.