I actually worked at Jeep body engineering in the early 90s. It was officially called a "sport bar" for exactly the reason you state, but it was fully engineered as a structural part of the chassis to provide roof-crush protection.I remember when JEEPs had roll bars, also know when 'they' renamed them to 'light bars', to avoid lawsuits.
I am of the opinion that ROPS is both - to prevent rolling beyond sideways in all but the steepest terrain, and to provide some operator protection in case it does. But this is all armchair quarterbacking, to be fair.