Why, isn't much simpler?
- Most flights are delayed or moved up due to winds, commonly by 1-2 days. When they say to get on the plane, you have no choice - even if it's Shabbos. And most flights are on weekends, so the chance of you being forced onto a plane off Antarctica on Shabbos is incredibly high.
- Ships that operate fly/cruise cannot accommodate kosher food due to stocking issues and schedules.
- After your tallis/tefillin and a change of underpants, your baggage allowance is too small for a tuna sandwich, let alone a week's worth of food.
Shall I continue

?