Very steep stairs would be a defensive advantage. Presumably, if the enemy got inside the walls, the defenders will be at the top of the stairs, so steep steps, maybe even not quite long enough for your entire foot, would put the attackers at a severe disadvantage.

Regarding the swinging portcullis, it's possible that the gate has hinges at the top and swings down from the ceiling. You might see something of that sort if the portcullis was a late addition to the fortress. Perhaps the original architect considered the main gates to be sufficiently strong as to not need an additional gate, or whoever built the castle did it on the cheap, cutting out some features in favor of a more luxurious bedchamber or something.