Because they came here not to better their lives, but to ultimately create an anschluess of the American Southwest and whichever else they can grab to Mexico.
There may be second generation Mex-Americans who support
unification with Mexico because they have been exposed
to American liberal education and have no idea how rotten
and corrupt Mexico really is. And, there may be politicians
and leaders in Mexico who think by overwhelming the SW US
with poor Mexicans they can force the issue eventually.
But among the masses of illegal aliens there is no
conspiracy to turn the Southwestern US into “Alta Mexico”.
Anyone who would believe that these farm and factory workers
are sophisticated enough to actively involve themselves in
such a conspiracy will believe anything. There is enough
genuine bullsh!t going on to occupy our thoughts and efforts.