First, because we have too many immigrants already and only a small fraction of them have come from South of the border. Second, because every story you’ve ever heard about how great it is here was a lie. Plain and simple. We have fire ants in every back yard, scorpions, rattlesnakes and tarantulas all over the place, and cockroaches as big as your hand. And there’s more:
As TexasDoubleDoc, a commenter at Instapundit, says: “The grocery stores only stock potato chips and coke, the roads are full of potholes, and gunfights break out every twenty minutes. The schools are in shambles, there are regular book-burnings, and everyone is forced to attend [a Baptist church] every weekend.
“Women have zero rights here, gays are stoned in the town square, and minorities must apply skin whiteners to blend in and avoid violent mobs. There is no true ‘nighttime’ here, as Texans frequently burn large open swaths of oil for fun. And EVERYONE rides a horse, so it stinks to high heaven from all the manure on the disintegrating roads.”
Plus which, there are no more jobs left anymore. None at all. Zip. All taken. So do us all a big favor and stay the hell away. Pretty please.
THE TEXAS SCRIBBLER 
I think any Northern Emigre should be required to have a special chip implant. The second they utter the words ‘The way we did it up North was…..’ ; they would instantly be zapped back to Wisconsin or Ohio or North of I-40. Whatever. The way we do things in Texas is the way we do things. We don’t need no steenkin’ hep.
Why did you only enumerate only the fun stuff?
Fighting off the giant cockroaches with your shoe isn’t so fun. Or checking your pants legs every so often for tarantulas and scorpions.
“We have fire ants in every back yard, scorpions, rattlesnakes and tarantulas all over the place, and cockroaches as big as your hand.”
You should lean on another point more: now you have a lot of ex-Californians all over the place 😉