At least in the Martian Chronicles, all the
colonists had the resources of the planet
and a whole planet with an atmosphere
to roam about on.
The ISS people are dependent upon finite
supplies and a dependable source of
resupply from the earth, and have no
atmosphere other than what's artificially
created by the ship itself. If there's any
failure of the life support systems of the
ship, they're all toast. Can't send up a ship
load of food ? Toast. Can't clean the pee
out of your space suit ? Toast
Etc. Etc.
