I am still puzzled by the original *The Planet of the Apes* movie from the 70's. How come that sentient species invented weapons, but was unable to develop powered flight, or spacecraft. Thus, the question is:

**What could prevent a sentient race from going to space?**

Assume an earth-like planet, and human-like species. This race should get through similar history build-up as humans, with one twist: They should not go to space.

What is most obvious factor to prevent them to go to space? 

By "space" I mean not being able to pass [first orbit][1], and never launching satellites. But otherwise, I would like to get this race to at least Earth 70s technology level.

This planet has all the resources needed to get to the space (basically think of alternate Earth)

  [1]: https://www.youtube.com/watch?v=RKs6ikmrLgg