There's no real story. Counties govern themselves, and the Constitution prohibits the Legislature from "regulating the affairs of counties, cities, towns, wards or school districts." Tex. Const. art. III, sec. 56. So in kinda the same way that Congress cannot have a law that applies only to Alabama, the Constitution does not permit the Legislature to legislate for each individual county.
So the Legislature gets around that through inventive definitions typically tied to population and/or geography. And yes--they do go in once every ten years and have a housekeeping bill to update those population numbers. But I don't know whether they're going to have a housekeeping bill to update the name of the Gulf of Mexico.
For my part, I'm not saying shit about it. Until one day, when it benefits a client. At some point, I'm definitely filing a summary-judgment motion saying "this law doesn't apply to my client because there ain't no thing as no Gulf of Mexico, you America-hating libtard."