« D’est en ouest » is an idiom, but directions use an article (le / l’) in all other contexts. Therefore, de nord en sud is totally unheard, as would any other mixed things like d’est à l’ouest.

To make it clearer, here’s an equivalent for north–south :

from north to south >>> du nord au sud (only possibility)

and east–west :

from east to west >>> d’est en ouest (first possibility, using the idiom)

from east to west >>> de l’est à l’ouest (second possibility, *regular* way, though rarer)