Mars isn't the closest starting point. Asteroids are. Some are far closer, and even those in the belt are easier to reach than Mars because you don't need atmos

Mars isn't the closest starting point. Asteroids are. Some are far closer, and even those in the belt are easier to reach than Mars because you don't need atmospheric braking and a ton of fuel on your return flight just to get back out of the gravity well. And the asteroids provide us with more livable habitats and access to far more resources.