The rolling luggage is primarily useful in the vicinity of airports. Inside airports there were no curbs. And I don't think people are going on long journeys through downtown areas with their luggage. I think you have a better argument asserting that rolling bags were facilitated by cheap polyurethane skate wheels.

There were fewer ramps and more stairs in airports and their parking garages prior to the 90s, due to the ACA.

And people drag luggage around on city streets all the time. Many tourist destinations are pedestrian cities even outside their most central downtown areas. And luggage also needs to be dragged around hotels — and in suburban areas their absurdly large parking lots.

The skate wheels are a plausible argument, though.