I’m slow off the mark. I figured out why the el paso shooter drove there.
That walmart is not far from a border crossing to/from Juarez.
Mexicans are prohibited from owning weapons. Even having an empty bullet casing can get jailtime there.
They came over for weekend shopping and were literally sitting ducks.
In Dallas the shooter’d have been ventilated quickly. The unarmed Mexicans citizens who likely (most of them) lived in Mexico (and were unarmed) couldn’t shoot back.

What about the other border towns?
supposedly, you are not allowed to enter Walmart concealed carry.