Speculation is that they did this so that people don’t just steal Lae’zel’s armor or Shadowheart’s artifact on the ship while they are not full party members yet. Not a very good solution.
Especially since it does not prevent you doing this - and in fact does not prevent any of the various exploitative behaviour at all. The only thing it
Actually does is that it prevents you from setting up Shadow's prepared spells, and stops you from having those characters use items (like potions).
