[gridspy]

Perhaps wheels on a suitcase required modern plastics?

[Merrill]

I think that the first wheeled suitcases used indoor roller skate wheels. So the parts were readily available for a long time before wheeled suitcases.

But early airports didn't have miles of corridors and a hundred gates, so maybe the need wasn't as great.

[danesparza]

We had wheels on cars, baby strollers, and bikes before the moon landing.

The cold war re-prioritized life for many Americans (and Russians, too I'm sure)

[DocTomoe]

... because wheels necessitate plastic.