Launches, yes, but landings? Athmosphere is your enemy during launches, but your friend in landing.

Mars has an atmospheric pressure less than one percent of that of earth. That makes losing speed other than with rockets a problem, and that requires bringing lots of fuel.

In addition, the athmosphere that's there can be windy and turbulent. That can directly affect a spacecraft, but also causes dust storms that can make it hard to measure distance to ground.