One reason is in the article: less immigration does not lead to more native employment. I can also assume that it has no effect on salaries, too. There is an argument in there that more immigration => more jobs for the natives, but it doesn't say if those jobs are the same as the ones for immigrants, and I assume they're not, they're management jobs to oversee the immigrants.

As a conclusion, immigration does not affect low skilled jobs in any way. No matter what the politicians propose, increase immigration or decrease immigration, their situation is more or less the same.