Because its one if the few places you can be nearly 100% certain no one will fire back. Shoot up a restaurant, mall, church, park, etc you will receive return fire from lawful carriers almost immediatly, especially in Texas.
There are more guns in the US than people (some estimates have it at nearly 2 to 1). You cant stop people from getting them any more than the war on drugs stopped people from buying weed.
What really needs to happen is solving the root issue of violence. Poverty and a lack of access to healthcare (which includes mental healthcare).
its true, making something illegal and actually enforcing it has never resulted in less of that thing anywhere ever
these guns are not magically appearing in the hands of killers and these kids are not buying their guns through their extensive maffia connections
theyre being mass produced legally, imported legally, advertised legally, sold legally and carried legally at a scale that would be entirely impossible to match illegally
i honestly have no idea how folks can genuinely believe that letting mossberg and glock set up multimillion dollar factories and buy ads online, on tv or in the paper has 0 effect on the amount of guns in the USA, or that guns being a totally legal and normal thing for regular, law abiding dads to buy and own without having to contact their friendly neighborhood gang representative has no effect on the amount of kids getting their hands on them
it's so entirely ridiculous of a view to have that you have to be lying