A bit OT to your question, but a nod to "The Planet of the Apes" - ie. a civilization built on the ruins of an older one:
The older - "original" - civilization had already used-up some necessary resources or raw-material needed to allow space-flight to happen.
It wouldn't even be necessary for a particular resource/raw-material to be completely used-up, as long as all the easy accessible sources were exhausted... ie. what you could get at with primitive technology.
Nor would it have to be something directly associated with space-flight; it could just as well be lack of resources preventing them to reach a necessary technological level (eg. can't make electronics), or preventing them from making necessary tools (eg. computers or welding-equipment).
One would also expect that space-flight would come pretty late in their technological evolution, so if lack of resources preventing them from reaching prior steps - eg. combustion engines, air-crafts, plastics - space-flight may be difficult to achieve... and perhaps more important, difficult to imagine.
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What if some disaster - lets say a new ice-age - devastated our civilization, decimated our numbers, destroyed most our of knowledge, destroyed our machines... Could we start from scratch? With no easy accessible ore of iron or copper... with no easy accessible oil or coal... Remember oil isn't just used for combustion-engines, it's also used to make most plastics. I think it would be difficult to reboot our society - even though we would know it could be done and much about how.