I am still puzzled by original The Planet of the Apes movie from 70s. It still makes me puzzled how come that sentient species can invent weapons but not be able to invent aeroplane, nor spacecraft. So lets ask about it:

What can prevent sentient race to go to space?

Lets have 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" is meant not being able to past first orbit and not being able to use 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)