Chief: Listen up kay-dets. I'm here to spell out to you the care and feeding of a landing craft. One 'a you butter shirts may be honored by driving some of us Marines to the fight.
Cadet: What happened, Chief? Did the techie win the coin toss today.
Chief: Nah. He got a good look at the the coin I was using. Now future commanders tell me why Gawd in his infinite wisdom gave us special built ships to get us from orbit to dirtside? We have mastered the atom, the gravity force and superluminal flight. Why do we still rely on glorified SSTOs like our primitive ancestors?
Cadet: A teleporter will get you killed?
Chief: Correct. But not the answer to my question. Yes, there's over 167 separate meteorological and geological conditions that will turn your teleporter into junk or if you try to use it anyway leave you dead or a tale to keep your friends up nights. But why the need for shuttles, landers et al?
Cadet: Uh... our ships aren't aerodynamic?
Chief: Son, when you got a big enough fusion plant an asteroid is aerodynamic. Be specific please.
Cadet: An airframe takes up mass. It doesn't pay for a ship that will land on a mission maybe 5% of the time. Also ... even if you don't use them wings still need to be shielded and they increase volume, mass and power of the shields required.
Chief: Very good. I may let you drive me to the fight, you're so bright. Anyone else?
Other Cadet: And the Vasimir rockets we use don't work well in an atmosphere. You need to stick an air intake on the front and use your reactor to superheat atmospheric gas to create a jet. That takes power away from your shields and weapons leaving your ship more vulnerable in the air. When you're operating in space it's just more mass and more maintenance and cost.
Chief: Excellent. Yes?
Cadet: What about operating on or near a world like Luna? Light gravity and no air. You can use the main engines all you want.
Chief: Yeah. That's no place for troops. You can get roasted by maneuvering jets or cooked on the inside by sensor beams or squashed by thruster fields. On airless worlds we're either underground storming tunnel cities or ... we'll soon be underground either way. You ever see a battlecruiser 50 meters off the ground? I did.
Cadet: It must have been a sight Chief!