I’ve seen them say that things fall “because of density”.
Like we fall down because we are heavier than air.
Like they think they’ve avoided the problem but they haven’t.
You can make good reasons or at least plausible ones. 40k has planetary shields. There could be a civil war so neither side might want to destroy the surfaces of each planet and civilians. Battletech has spaceship tech being rare and irreplacable, and there are treaties limiting orbital and nuclear bombardment.
Sometimes the most realistic route just isnt fun though so i can usually look past the contrivances.