I fish in that area several times a year. I've seen some ill advised bikini and banana hammock wearage by people with very high BMI, but never anyone nude.
I think it is simply that you have to go pretty far down the beach to get away from where most people go, and the farther north you go, the less beach there is, and the more it sucks as a beach. Lots of shell, sand is brown and siltier as you go north, and water is rarely clear. Just too close to the Red river and Mississippi river backwash. TONS of mosquitos at night. But yeah, its the most isolated stretch of beach in Texas that's not on an island, so if there are nudists, they'd be out there. And they'd be the kind you'd never want to see...