It has nothing to do with the beaver theme gift shop and everything to do with those bathrooms being spotless and those soft drinks and gas being cheap.
All other gas stations in all other restrooms across Texas and across the US, is like playing Russian roulette. And you don't know if you're getting the bullet until you walk into that restroom. Most of them always smell like they've been mopping the floors in rancid piss for the last six months.