It is certainly true caravan wheel bearing fail frequently, but failure of similar bearings in other applications is very rare. Some of those other applications see far greater usage than the few thousand miles seen by caravans.
What happens with caravan bearings unlike almost every other application, is that they are disturbed at the annual service.
I don’t think you need to look any further to understand why caravan bearings fail so regularly compared to wheel bearings in cars, lorries, aircraft, and rolling element bearings in automotive gearboxes, aero gas turbines etc,
The list of where failure is rare goes on endlessly, but then they are not disturbed every year.
Some caravan owners have known both bearings fail, big message there. Possibly the same fitter serviced both wheels a year or two years earlier?