Why hasn't a space elevator been invented?

Because technology needed to make it doesn’t exist. Material for elevator cable has to be very strong and at same time very light. read more

While a viable space elevator might help reduce the cost of spending things into space it does not help with sending millions of tons of equipment and hardware to Mars. SpaceX will spend its money improving rocket technology and leave the massive R&D expenses of a space elevator to other companies. read more

A space elevator could easily get people and materials into space at a fraction of the energy and cost a rocket launch requires. Instead of burning expensive fuel to launch heavy objects off of Earth's surface, the elevator could convey them up the tether past lower Earth orbit and into space. read more