Long haul trucks have very limited space. Many truckers do bring a portable chemical toilet but it wouldn't really be practical to install a flush toilet like in an airliner lavatory.

I’ve witnessed the alternative and had to clean it off my shoe. Public bathrooms should be a right, if only for sanitary reasons.

An entitlement, rather than a right, but the problem again is who cleans these things up to a workable standard. Is a public facility worth much if clogged and overflowing with human waste? If antisocial actors spread such waste and other fluids on the walls? It becomes worthless as a public accommodation and so effectively ceases to exist again. Solution for public facilities is probably automated effective sanitation and/or a Singapore model of disincentives for being gross in public.

Or just do what we do when people shit on the sidewalk routinely: we pay people on the city payroll to clean it up. Governments can provide services for the public good; it doesn’t have to all be for profit or have a positive ROI. Governments exist to support the people. Forcing people to shit on the sidewalk is in nobody’s best interest.

Even in private facilities open to the public, the poo bowl isn’t kept very well at all, profit motive be damned. Cities do pay people to do this but either not enough people or not well enough paid cuz the job they do sucks too. I don’t know the answer but I don’t want to do the clean-up work myself, and I’m not sure I want the city paying what I would require to do the work. Robots, baby!