I noticed this in a recent story in Asimov's, but it's something I've seen in a fair bit of other sf as well:
In a science fiction story, say there are some soldiers on the surface of a planet, and say there's a spacefaring organization (such as an opposing military force) that wants those soldiers dead.
Almost invariably in sf stories, what happens is the spacefaring organization lands a bunch of soldiers on the ground and the two sides fight it out. And as often as not, the plucky fighters on the ground get the upper hand through courage and luck and authorial fiat and end up winning.
It seems to me that the incredibly obvious solution is for the spacefaring organization to drop things on the ground-based soldiers. If the ground-based soldiers don't have surface-to-air missiles or the equivalent, then bombs dropped from aircraft are sufficient. If the ground-based soldiers do have some sort of anti-aircraft defense, then rocks dropped from orbit should do the job.
Of course, that would eliminate the plot, not to mention the protagonists, of a lot of stories, so it's become a genre convention that combat has to be carried out on the ground.
But it's not a genre convention I'm fond of.
(Yeah, yeah, you can finesse it. You can say there are civilians present on the ground, or say there's a specific artifact/MacGuffin that needs to be retrieved rather than destroyed, or whatever. But most authors in my experience don't bother.)