i imagine the reason they aren't is because of lack of funding coupled with the enormous cost of such a journey + the logistical nightmares of keeping a crew of humans alive on a year-long round-trip journey to mars and back + the fact that spaceX is already taking huge strides in the space fieldmost things government does today have the capability of being done better by private enterprise. government agencies tend to be very inefficient at doing tasks than private ones. and we're seeing that very evident in SpaceX. nasa has not made any significant milestone achievements in decades and yet spaceX has been doing things over the past few years that NASA is still at least a decade away from doing (such as creating computer-controlled rockets that are intelligent enough to initiate a controlled descent burn upon returning to atmo, and land themselves on a recovery barge intact so they can be reused).
