Why aren't they on the same carbon?
Why is it drawn in a particular way (one OH 'up' and the other 'down')?
Or something else?
Why are they in opposite formation on different carbons instead of like on the same side but on different carbons.
and not like this: link
If so, they are both correct ways of drawing them - but the first one is more common as it's drawn as a straight chain like butane is here.