There isn't a plausible reason
Yours is an example of what I call a "technology dichotomy." Technology exists that depends on an earlier technology, but that earlier technology doesn't exist. This can't be so.
The technologies you describe depend on ground transportation. You could claim that the city jumped over wheeled, combustion automobiles and went straight to hoover craft or gravitics, but that's just sophistry.
The truth is you must move materials. Raw materials. Manufactured materials. Food, metal, wood, you name it. The amount of goods that demand transport for a high-tech society of any reasonable size (and you'd need tens if not hundreds of thousands minimum to support nuclear power and a space program) is astronomical. And before you had a space program and nuclear power, you had carts, which would lead very naturally to motorized carts (aka, automobiles).
And it's the nature of all things (from evolution to working in an office) to take the path of least resistance. If it's cheaper to build a wheel, you'll use it to pull potatoes, even if you have gravitics.
I'd say you were trying to put the cart before the horse, but in reality, you're trying to put space flight before the cart — and that's impossible.