By itself it means nothing. Lots of people who don’t speak English can sweep floors. However multiplied by 25 million and it becomes a bigger issue.
If immigrants come to the US in small numbers, they, or at least their children, are forced to learn English and assimilate just to function and survive. When you open the gates and let millions pour in across the border, they can set up their mini-nations (and eventually take over entire regions) where there is no need to do that. Good parts of the southwest are "USA" only in a legal sense. Culturally, politically, linguistically, and even economically, they are basically part of Mexico.
And theyll never do anything else until they learn English.