If US goverment was throwing money at NASA like they did with Apollo program, we would have base on Moon and manned mission on Mars long ago
But well... money - that's the main reason. There were programs and plans to land on Mars.
Orion capsule and SLS (Space Launch System) is right now in testing phase and that should get us to Mars
and
Give Elon Musk a few years and he will land there with SpaceX considering their progress