It really has nothing to do with the cleanliness of the showers or facilities it has to do with the people who hang around these and other such facilities. This is NOT a slam on truckers as they are great people or at least most are. We have several over the road truckers in the family. It has to do with the others who are there for one reason or another. I am retired LEO and have some experience with the situations that arise around these places.
I will add that two of my daughters walked from the motel we were staying in recently, across the street and across the truck stop fueling area (Loves)to an eating facility there. They came back commenting on the comments made to them, the wolf whistles, and other inappropriate actions when they walked the area.
Generally we warn against hanging around rest stops. Truck stops are near to them in problem areas.
Most are not problems but how do you know which one's those are?