If anyones ever been on a military ship, the amount of space in most of the areas are quite confined, any discharge or weapon has the chance for to ricochet, causing harm and damage to other people and things.
The size of even the small Imperial escorts dwarfs the biggest fighting ship we've put to sea. And they don't seem all that stingy with space.
Corridors where multiple men can fight shoulder to shoulder. Cathedrals multiple stories tall. The lower decks are an entire city unto themselves with their own economies and societies.
The ricocheting thing might have some weight, though. I know in Necropolis
las rounds were ricocheting in the street. That could also happen on a ship, I suppose.
On the other hand of things...Space Marines who are really built for boarding actions and equipped for it, don't have any sort of boarding specific range weapons, do they? And the regular weapon of a space marine is probably heavier hitting than anything outside a crewed weapon a normal human would use.
True Space Marines are proofed against the void (until their armor is penetrated...) but void suits are hardly rare. And plus if you're a few dozen decks deep, the chances of being let out into the void is pretty slim to none. In fact, if a shot managed to open up that much hull, there's probably bigger worries than your las gun hitting something it shouldn't.