Mars is an interesting nut because even if we shortened the trip to Mars, it is arguable we've made the problem of the trip even harder. Unless I'm mistaken, the soonest we can leave Mars is about one year after leaving Earth (and that is assuming a certain velocity, if we are traveling quicker, presumably we have to wait longer on/in/around Mars). Arriving at Mars quicker doesn't actually gain us anything unless we can live on (in?) Mars. And living on (in?) Mars is way way way down the road.
This isn't Pikmin, where we have infinite power to ascend back up to the mothership every day, and there are no fruit for us to harvest.