The "Weisswurstequator" - a rough dividing line north of which the white sausages just aren't a thing - also largely applies to soft pretzels.
They are popular enough all over Germany for them to be sold in virtually every bakery all over Germany. Weißwurst, on the other hand, is only available in specialty restaurants (though I assume it's sold in all large supermarkets). Having eaten both, it's not hard to understand why.