Space vampires would suck
Ok, so imaging you’re going to play Planescape or any other sort of space adventure that uses D&D. You than hear there’s a lot of freedom to chose what your character is because there is a lot of unique races in space, so you initially chose vampire. You than remember that vampires can only be out at night because of the sun (I.e you can only be out when the earth (which is a sphere) rotates to were the place you’re standing is not facing the sun). But if you were in space you would have nowhere to hide as there are suns and brighter stars literally everywhere, so space for a vampires is essentially a death sentence or you exists is a never ending realm of fire and torment.