About disposal, don't you get little hygiene bags to store the ickies? So why not just carry them off them off the hill like you would normally rubbish?
Good question, but now imagine yourself on the side of Ben Lomond or similar realising you need to change your protection. There are people around and no cover. Do you wait and risk an embarrassing leak or do you do it in public, or go off the path a bit hope nobody is looking. Or do you just stay home. Of course you can carry them out, but there's more to it than that.