How do you figure? Lack of will? Technology? Cash? What?
All of the above. For one, it would take a year to get a spaceship from Earth to Mars. You’d have to resupply it several times along the way. Even if you could do it, which is highly doubtful, it would cost a ton of money, and the astronauts would not be in any physical condition to perform the mission when they got there, much less be in condition for a one year return flight.