those panels are more cost efficient because you can manufacture and then install them with poorer tolerances. the panels being smaller in general also means they cost less in materials to manufacture. and then, as a bonus, they allow the floor to be cleaned/mopped easier.
McDonald's usually has good, reliable bathrooms fyi. That and truck stops (not gas stations, the ones that have big lots for truckers to sleep in overnight). There's also an app whose name I forget like places I can poo where people rate public toilets.