It breaks up the monotony of road trips and thus is remembered fondly. Instead of a boring gas station where you just go in to grab a drink, it turns it into a destination and an experience that sells camping equipment, merchandise of the mascot, hot food options, a miniature section of random home goods. They say it's about the journey and not the destination, but in long road trips, the only part of the journey where anything happens is Buc-ees. And thus you get brand loyalty after a single visit and next thing you know you're wearing a Buc-ee hat everywhere and going 30 minutes out of the way just to stop there.

Also actually clean restrooms.