Why is SpaceX focusing on rockets and not on the space shuttle? Well, for one, the Space Shuttle was retired, so why would SpaceX focus on a non-existent program?
The Space Shuttle did a lot but was also the most deadly of all of NASA’s manned space flights. More people died on the Shuttles than at any other time before or since. Six people died when the Space Shuttle Challenger blew up shortly after launch, killing all aboard. Another six people died when the Space Shuttle Columbia burned up on reentry over Texas.
That is why President Obama wanted to retire the Shuttle program and concentrate on getting a human on Mars. This vision is still supported by the new President until he figures out it was Obama’s vision (because he hates Obama) and cancels the program.