In Germany, there are free restrooms on autobahn parking lots (essentially truck stops without a gas station or shops or anything, just the restroom) and these paid restrooms. The paid ones are objectively miles ahead in terms of cleanliness.
(Every once in a while you also see free restrooms where the cleaning person asks for a tip.)
In France, the gas station restrooms on highways are free and they are clean (the restrooms in rest areas without a gas station are more hit and miss) so it's more a question of being within a building with employees being there at all times, I would think.
In Belgium, you'd better not need to pee on the highway on Sundays or at night because the restrooms (paid, or reserved to clients of the restaurant/shop owner) are simply closed, outside of a handful of gas stations where they cost 0,80€ AND are only moderately clean.
In the US we have free gas stations along our freeways. I've never stoped at one on he Autobahn so I can't compare, but they sound like the same idea. They are run by the state and in general clean and nice (there are exceptions). Gas stations are hit and miss - most of them are also nice and clean, but some are disgusting.
I was at the train terminal in Paderborn (visiting Germany) and did not see the sign that "suggested" paying to use the restroom—but the attendant did not miss that I didn't pay and almost assaulted me. When your German is rather limited it's sort of difficult to understand when someone is screaming at you...
(Every once in a while you also see free restrooms where the cleaning person asks for a tip.)